Mousse has long, black hair which is either past shoulder length in the manga or waist length in the anime and teal eyes . He wears a long, white robe with a diamond pattern on the chest with black cuffs and voluminous sleeves from which he produces his arsenal of hidden weapons. Underneath this he wears black or dark blue pants.
Characterised by his extremely bad eyesight, Mousse has to wear Coke-bottle glasses that are so thick that his eyes cannot be seen when he puts them on. He tends to have them propped up on his forehead or concealed in his robes, leading him to commonly mistake other things or people for the person he is trying to talk to (e.g. Ranma or Shampoo) or grab onto (Shampoo), even when the subject he is looking for is close by.
Mousse is desperately in love with Shampoo, and has been since they were both three. He thus sees Ranma Saotome as the rival he needs to either defeat, surpass, or kill in order to win Shampoo's affection. According to Cologne, however, Shampoo's rejection of his proposal at that time will still hold true regardless if he manages to overcome Ranma. He is also one of the few, if not the only (main) young male character not to be in love with Akane Tendo.
He was cursed at Jusenkyo to turn into a duck, having accidentally walked into the Spring of Drowned Duck due to his poor eyesight. According to the Jusenkyo Guide, he is the first person to ever fall into a spring after taking only one step. Even in the form of a duck Mousse can still make use of many of his projectile weapons, such as knives and bombs. Somehow he manages to hide the weapons in his feathers while his duck form, making him one of the very few cursed characters who is not completely defenseless while in his cursed form.
Mousse's vision appears to improve greatly while he is a duck, but this may be because when he is in his cursed form, he has to always wear his glasses, with which he can actually see well enough in both forms. However when a jizou statue blatantly disguised itself as either Shampoo or Ranma, Mousse failed to see any difference from the originals even while wearing them, (however lack of sleep could have contributed to this). Unfortunately for him - either on reflex or to appear cooler when making an important statement - he tends to take off his glasses and thus embarrasses himself when he talks to the wrong addressee.
It is proven that, despite his obsessive behavior, Mousse truly cares for Shampoo's well-being. In the last story arc of the manga, Shampoo is enslaved through the use of a magic egg that exaggerates a hatchling's imprinting instinct. This occurs a second time later in the arc, and Mousse is offered the chance to make her his slave. Instead, he uses a mirror to imprint her on herself, granting her free will. Unfortunately for Mousse, she immediately resumes her pursuit of Ranma without even thanking him, and he remarks that he will be kicking himself over this decision for years.
This should be seen in relation to that Shampoo repeatedly attempted to enslave Ranma through a permanent love-inducing pill, and later casually confessed to him (during Akari's introduction story) that she would have used any similar magic long ago if she possessed any.
He hasn't been above occasionally using dirty tricks or traps to succeed, and in an early appearance he thoughtlessly almost skewered Kasumi when attempting to snare and kidnap Akane, as well as some children when aiming for Ranma, but he turns more considerate towards the end.
He's shocked at the prospect of 'just' running into some kids with his bike, although after he noticed that they looked exactly like Ranma and Ryoga, he reflexively bumped their heads together. He has apparently refrained from using dishonourable methods after they almost caused Shampoo to lose what little respect she had for him (his superior skill and enormous resolve to never give up), and Ranma embraced the practice to even sillier extremes.
He has also displayed nearly limitless tenacity and dedication when fighting for the chance of 'winning' her affection, even if she callously sabotages his prospects, or Amazon law apparently doesn't grant him any automatic rights through overcoming either her 'groom' or herself. It seems more like a case of proving his worth.
Mousse dislikes Ranma with a great intensity, but at the same time seems to be developing a more relaxed rivalry with him, much like Ryoga did. He has gone as far as to help him on a few occasions, like during the fight with Pantyhose Taro, the confrontation with the Musk Dynasty warriors, and the final battle with Saffron.
However during the first two occasions he initially planned to betray him, and the third time he was largely motivated by the draining Jusenkyo springs and (later) to free Shampoo from their slavery. Regardless, he did help to save Ranma's life in the latter two instances.
Towards the end of the manga, when both Ranma and Ryoga were turned to kids by a magic mushroom, simply seeing their likeness maddened him enough to reflexively slam their heads together, so he apparently holds an antipathy towards Ryoga as well, perhaps due to his constant defeats at his hands. However, they initially collaborated to get a cure for themselves only during the initial Musk chapters, and he was briefly upset when he and Ranma thought Ryoga had died in a fissure caused by Herb. Here he also saved Ranma from one of Herb's killing strikes to repay his debt for Ranma's assistance to unlock his duck curse. During the Saffron arc he Ranma & Ryoga also all watched each other's backs through collaborative teamwork.
His first objective remains to win Shampoo, but not necessarily by going through Ranma. Mousse was enthusiastic at the prospect of seeing Ranma and Akane get married. In the final season of the anime ("Let's All Go to the Mushroom Temple!"), he pitted himself against both Kuno and Ryoga to prevent them persuading Ranma & Akane to take the antidote to the love-inducing mushrooms they had eaten.
He hasn't interacted with Kuno in the manga, but they accidentally allied against Ranma during the Hiryu Shoten Ha story. In the separate anime continuity he and Ryoga teamed up against Ranma once, although this was mostly Mousse's idea. Here, he also trained together with Ranma, Ryoga and Kuno to beat copycat Ken, and initially allied with Ranma and Ryoga in the episode "Back to the way we were ... Please!". However, even here Mousse apparently isn't a good acquaintance of either Ryoga or Kuno, and the episode "Back to the Way We Were ... Please!" noted that Mousse is too occupied with training to have made any friends.
Mousse generally gets along with Cologne, although he tends to annoy her by mistaking her for Shampoo. Cologne, on the other hand, does not attempt to restrain Mousse from his pursuit of Shampoo, but clearly favors Ranma as a more favorable match for her.
Ranma and Mousse are rivals for Shampoo's affection, although Ranma really doesn't want her attention. Mousse was one of those who eagerly took advantage of Ranma's weakened state after the latter was afflicted with the Ultimate Weakness Moxibustion but was stopped by Ryoga. After he obtained the Lens of Invincibility, Ranma was the only person he deliberately used it on after accidentally discovering its powers by using it against Cologne. After learning that it was the lens however that forced Ranma to grovel before him and not his own abilities, Mousse was about to stop using them until he overheard Ranma call him a hopeless cheater. He then used the lens two more times before deciding to fight fairly and preserve his honor. Despite Ranma's stooping to use various Joketsuzoku items designed to enable weaklings to fight stronger opponents, Mousse swallowed his pride and used the lens on himself to force himself to apologize before Ranma and allow himself to be defeated in a fair fight.
Nonetheless Mousse and Ranma normally get along well enough to treat each other civilly. It is suggested that despite his attempts to kill him, Mousse does see Ranma as a friend as he helped him rescue Akane Tendo when she was kidnapped by Pantyhose Taro, and prevented him from transforming into his cursed form, although this may have been simply because Mousse wants to be the one to beat up Ranma himself. Mousse also joined Ranma to recover the Water Pot of Liberation from Horai Moutain, although he and Ryoga at first planned to eliminate Ranma on the way to get rid of their greatest love rival. He later teamed up again to help rescue Shampoo from the Phoenix People.
Mousse originally kidnapped Akane in order to get to Ranma so he could finally defeat him but ultimately failed. The two don't interact with each other much throughout the series, but they seem to get along and are able to agree on certain points. Akane was also the only person Mousse told about the Reversal Jewel when Shampoo was under its effects, showing that he has some trust in her.
While Mousse and Ryoga don't interact very often throughout the series, they do tend to get along whenever they're together as they have trained alongside each other and hung out (as a group) with the others. Though it should be noted that in Mushrooms of Time Arc he claims to hate Ryoga just as much as he detests Ranma.
Fighting Style: Mousse is an extremely proficient martial artist and is skilled in several systems, presumably including the acrobatic and flexible Joketsuzoku style used by the other two Amazons, Shampoo and Cologne. He is a master with practically any weapon, and is very agile.
Mousse fights using hidden weapons (Anki 暗器), which includes roped hooks, rope darts, iron balls, handcuffs, hidden knives, bombs, and even training toilets, and all hidden in his long sleeves and robe. The reasoning for this is supposedly dark magic which in the Ranmaverse is hiding things where it is dark. Mousse has been shown though to not have an infinite supply of weapons in his cloak. Additionally, he's quite crafty, and is able to make complex fireworks or actually plan traps to defeat Ranma.
Although he is a highly talented hand-to-hand fighter, Mousse prefers to use his mastery of the hidden weapons style to fight at a distance, where his naturally expert marksmanship can be put to better use. By using his full arsenal in combination with his considerable speed, he has managed to compete even with Mint, who may be the swiftest character in the entire series, although he had to use trickery to actually prevail.
Physical Power: Towards the end of the manga, he also received a remarkable strength boost through constantly dragging around a heavy sentient jizou statue, and afterwards managed to split a large iron bell with a single barehanded blow, which was enough for Ranma to apparently view him as considerably physically stronger, but it likely still doesn't compare to Ryoga, who can throw a few hundred tonnes with ease. It is unclear if this strength remained afterwards, but given that similar power-ups for Ranma and Ryoga did, it seems very likely.
Stamina: He has also displayed impressive endurance. As mentioned above, he continued to fight until his last breath, despite being caught in numerous explosions, to the point of being immersed in a smoking crater. Like Ranma and Genma he also just caught minor bruisings from falling many hundred meters into solid stone (Ryoga apparently received none whatsoever), and he's been stated to possess a much stronger tolerance to blunt impacts than Saffron, since the latter had been pampered all of his life, while Mousse has honed his stamina through constant sparring. In the anime, during his fight with Torristan, he was able to expand his muscles to remove many steel knife-like feathers from his body and defeated his opponent with a single punch, despite being so exhausted that he collapsed immediately afterwards. In the episode "Mousse Goes Home to the Country" he beat Tatewaki Kuno barehanded in 2 seconds, while Ranma and Ryoga usually take a few minutes to prevail in this continuity.
Limitations: His greatest weakness, despite his remarkable abilities, may be his own eyesight. Even with his glasses he was unable to discern the blatant disguises of the sentient statue. Despite this, his aim has proved sufficient to intentionally hit female Ranma's entire outline, when the latter was tied up in a circus, and even without them he managed to snare the Kinjakan in mid-flight. Through the use of his unique fighting style, combined with the ability of flight, his duck form remains quite formidable in combat as long as he keeps his distance, and attacks with blades, chains or bombs from afar.
Strictly speaking of their comparative mettle in serious battles with Ranma, he appears vastly more dangerous than Shampoo herself. When sufficiently motivated, he has displayed highly dangerous prowess. In his first battle with (female) Ranma he had the upper hand despite severely limiting the use of his arsenal. In his second major battle with (male) Ranma he came extremely close to prevailing, despite the handicap of being assaulted by Shampoo's explosives from the sidelines, and barraged his nemesis with an arsenal of weapons, to the point of making the latter fear for his life. He also reached a draw in staff fighting during the onsen race, and seemed to have the upper hand despite being exhausted during the referred jizou story.
However, he does not seem to be quite as swift or skilled in unarmed combat as either Ranma or Ryoga, and has been consistently beaten despite the advantage of using a barrage of bladed weaponry against mostly bare-handed fighters. He has repeatedly been overcome by the former, and when confronting the latter during the onsen race, Ryoga easily waded through his barrage of weaponry, and swiftly prevailed. When Mousse was teamed up with Tatewaki and Kocho Kuno, Ryoga also effortlessly simultaneously parried their attacks, disarmed and defeated them all in 1-2 seconds, but in this instance it could easily be argued that Mousse was taken by surprise, although Ranma later boots them all away after having his strength restored.
That said, he came extremely close to beating Ranma on three separate occasions, despite handicaps in each of them (No weapons arsenal in the first major fight; Shampoo threw bombs at him or handed him defect weaponry in the second; and he was extremely tired after carrying around the dougi, although that wasn't really much of a fight), and one hit from a sufficiently strong sword might be all it would take to win permanently (at least in Ranma's case), and he has not been truly tested since apparently turning physically stronger than Ranma himself.
Mousse's hidden weapons techniques allow him to occasionally overwhelm opponents with the sheer number of items he can produce, and barrage them from a certain distance.
Hidden Weapons: Mousse is a self-proclaimed practitioner of "dark magic," which is actually just hiding things up his oversized sleeves where it is dark. Mousse is able to keep almost any item imaginable in his sleeves and never seems to run out of room. This likewise holds true in his much smaller duck form, which has been seen swiftly dispatching throngs of projectiles cumulatively greatly surpassing its' own volume. This recurrent manga and anime phenomenon has commonly been labelled hammerspace. Mousse's attack of choice is a discharged throng of cutting or bludgeoning weaponry fastened in entangling ropes and chains, with a few silly items, like yo-yos, thrown in for good measure.
Smoke Bomb: A great fog, which simultaneously works as tear gas, as sneezing powder, and hides his whereabouts. It has set up the following attack.
Exploding Chicken Eggs (雞蛋拳 - Keiran Ken): Mousse pulls a chicken out of his sleeves and it quickly lays eggs into his hand. When thrown, they become similar to grenades, exploding when they hit their target.
Fuse Bomb Barrage: His duck form has also thrown a throng of small regular explosives, without any time delay involved.
Scythes of Sorrow: Used in Mousse's second fight with Ranma. It involves wildly slashing at his opponent with scythe-like blades from his robes. Additionally they can be used as projectile weapons.
Hawk's Talon (鹰爪拳 - Takazume Ken): Large, sharp claws appear on the tips of Mousse's shoes as he jumps far into the sky and then plummets toward his opponent. He stated that it is taught to a single student per generation.
Fist of the White Swan (白鳥拳 - Hakucho Ken): This technique is similar to his others. Mousse removes the "White Swan", in this case a swan-shaped child's training potty, from his sleeves and hits his opponent with it. He usually draws it out, swings it, and then quickly hides it again so the potty cannot be seen by his foe, representing the swan's graceful but unseen swimming.
Fire breathing: Likely the technique used in real life. Mousse never made use of this move in combat, but has nonetheless mastered it.
- Despite the fact that Mousse's parents are never mentioned in the manga, in the anime his mother once sent him a letter asking how his progress with Shampoo was going.
- Mousse speaks with a Tōhoku accent in Japanese.
- He is called "Muso" in some foreign language dubs.
- His voice actor provided the voice of Garamaru from Takahashi's subsequent series Inuyasha.
- His English voice actor provide the voices of Yūsaku Godai in Maison Ikkoku and Nobunaga in Inuyasha.