Many years ago Soun, along with Genma Saotome, was taken as a student by the founder of Anything Goes Martial Arts, Happosai. However "training" largely consisted of the grandmaster gleefully abusing them as slaves or pack animals, chaining up, starving and taunting them by eating all their food, and sticking them with responsibility for his thefts and runaway restaurant bills. They eventually managed to temporarily get rid of their tormentor by getting him drunk and then sealing him within a cave, by means of explosives, a large boulder, and a shinto O-fuda seal.
At some point Soun established his dojo, got married, and became the father of Kasumi, Nabiki, and Akane. With the untimely death of his wife, he was left with the responsibility of raising his three daughters and the duty of keeping his dojo afloat all by himself.
In traditional way of carrying on the legacy, there has to be a man to succeed him as master, so Soun struck a marriage arrangement with his old training partner. The latter's only son, Ranma, would marry one of Soun's daughters, and thus preserve the future of their martial arts style.
Soun let his daughters decide amongst themselves whichever should take up the engagement. But after Ranma's gender-bending nature was exposed, the two older sisters foisted him/her on Akane. However, due to a misunderstanding when Akane first saw him as a naked stranger awaiting her in the bathroom, she initially found this unacceptable and loudly objected. Despite this initial outburst, Soun and Genma remain confident that they will grow to love each other with time.
Soun is a middle aged man with shoulder length hair and a mustache, which he did not wear when he was younger. He is usually seen in a medium coloured gi (brown in the anime).
Soun is very emotional, and is prone to visibly displaying this, whether it be a tragic, happy, or angry occasion. He is regularly brought to tears when caught up in sentimentality, compassion, worrying about his children, or if he thinks their affection is in doubt. They occasionally gush from his eyes.
Soun still mourns, and is extremely loyal to, his deceased wife. He has a traditional Japanese altar devoted to her memory somewhere in the house, prays for her every year on the day of their wedding anniversary, and visits her grave in memorial of her death. However, he remained capable of joking about it to lighten up the mood, when offered compassion by Hinako Ninomiya.
His relationship with Genma comes under strain as the latter is wont to severely mistreat his wife, Nodoka Saotome, which Soun naturally finds outrageous. He was similarly upset after learning that the latter invented martial arts schools intended for burglary. In the manga they are not explicitly implied as friends, rather than fellow previous training partners, as they don't seem to independently interact much socially. They had neither seen nor heard from each other in many years at the beginning of the story, and Soun was initially shown as unaware of what Nodoka looked like. They seem to be on more friendly terms in the anime and frequently play shogi together, though Genma tends to cheat. Soun cheats as well though, so it could be that both of them do so as a way of training together.
Soun's wish to maintain the school legacy and occasional cowardice in confronting Happosai both mirror Genma's, although he has also been willing to stand firm against and attack Happosai on several occasions, sometimes by himself, and forcefully strangled the latter in wrath when he had apparently crippled Ranma for life with a 'weakness moxibustion'. He can be quite ruthless towards his old master, having attempted to kill or post him to the North Pole, but can also show pity and help him, depending on the situation.
Unlike Genma, he has also been portrayed as mostly honorable and a generally good person, frequently showing compassion towards others and offering hospitality or aid for people in trouble. He was willing to assume responsibility, as the master of the household, and apologies to Hinako upon finding her and Ranma in a very compromising bedroom position.
He's also acted as referee for formal martial arts matches. In many instances, he has worried about Ranma's welfare when overviewing them, and determinedly stepped in to interfere when the latter was about to be strangled to death in his confrontation with Ryu Kumon, and tried when Akane was about to be struck unconscious by the Dojo Destroyer, but in the latter case he was stopped by being bumped on the head by Ranma's suddenly entering bicycle.
He tends to become very angry whenever he suspects that Ranma is 'cheating' on Akane or otherwise is treating her badly, being intensely paranoid in this regard. Soun wants nothing less than the best for his daughter, and looks forward to the day she and Ranma will marry. He has become similarly intensely furious and overprotective when hearing the very notion of striking Kasumi, even to get rid of an oni possession leading her to poison and scratch his back bloody. He apparently constantly forgives Nabiki for any misdeeds, as he's never shown to hold a grudge beyond the initial shock or treat her less than charitably afterwards. When enraged, he displays a giant battle aura, frequently in the form of a giant demon headed version of himself, which most people, except Happosai and his daughters, find very intimidating. While quite old-fashioned in some respects, he honestly cares very much for his daughters' well-being.
The trait that is most taxing for Ranma's and Akane's nerves is his willingness to openly talk about their relationship. He has no trouble loudly expressing the very awkward couple's feelings for each other, and is completely oblivious as to whether this creates conflict between the two. If they lash out against each other in the face of his enthusiasm, he sometimes turns sad and confused.
Despite his flaws, Soun is a respected member of his community, and is regularly approached to take care of unusual problems, like apprehending assaulting pigtail-cutters during the Dragon's Whisker arc, help get rid of an oni when Happosai first appeared, or later when the grandmaster terrorised a tourist resort as a thieving and molesting 'octopus jar'.
It is assumed that Soun has some stable job or another source of steady income. He's never explicitly seen training students, although this may simply occur off-screen. In the separate anime continuity, however, one episode revolves around the fact that the dojo has no students at all, leading to monetary troubles. Soun has also complained about the costs of hosting two freeloading house guests, but conversely has not pushed either Genma or Ranma to somehow earn their keep, although Genma briefly worked for Tofu Ono. Soun likely earns money from the recurrent monster or troublemaker hunts, and has rented out the dojo, and had Kasumi serve food, for a local ladies' club meeting. He doesn't mind occasionally treating his family to dinner, or a vacation by the sea, but does complain about money troubles in the anime. In the manga he is mortified when Nabiki spends his meagre savings on expensive gifts for herself, or when a battle between Pantyhose Taro and Rouge repeatedly made holes in the house. In the latter case the family handled the repairs themselves, rather than let a craftsman look at it, despite Akane's being shown as very lacking.
Soun seems fully aware of Ryoga Hibiki's piglet curse after watching the latter change in front of him in the bath. He was completely unsurprised when seeing it again during Taro's introduction story. Despite knowing this, he doesn't seem to mind that Akane keeps the former as a pet, and allows him to sleep in her bed at night.
As a former student of Happosai, Soun is in perfect shape, frequently fights wearing full traditional samurai armor, and is skilled at both hand to hand combat and handling a wide variety of traditional weapons. He has been able to reach a draw against Ranma in serious bokken fighting, and has repeatedly kept the latter on the defensive when chasing him in a wrathful mood (though in the latter cases Ranma may simply have felt obliged to not retaliate, due to being provided with room and board at Soun's expense). He is usually effortlessly beaten by Happosai, but there have been a few confrontations between them where he has come across as quite formidable. In some episodes (128 - Scribbled Panda, 140 - Pick a Peck of Happosai), Soun demonstrates the ability to grow to Godzilla-like heights to fight enemies.
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- The name Soun means "already, now, fast, early" (早) (su) and "cloud" (雲) (on).
- Soun's surname Tendo means "sun, heaven, providence, way of heaven, destiny, divine justice/divine guidance/divine intervention, fate, fortune, chance, predetermination, lot" (天道), which literally means "the laws of heaven and nature" altogether.
- Soun's seiyū provide the voices of Daija of the Inuyasha.
- Soun's English voice actor provide the voices of Master of the Maison Ikkoku and Sesshōmaru of the InuYasha.