Yoiko Hibiki (響 よいこ Hibiki Yoiko?) is an alias Ranma assumes in order to get back at Ryoga for using him to get back to his home so that Ryoga could effectively go on a date with Akane when she comes over to see Shirokuro's recently born puppies.
"Yoiko" can be translated as "good girl", which reflects Ranma's attempts at being a good sister for Ryoga. Hibiki is translated as "to echo" or "to resound", which is more in reference to Ryoga's abilities in comparison to Ranma as than to Yoiko herself.
Ryoga Goes Home
After learning that Ryoga used him so that he could have an effective date with Akane, Ranma decides to get back at Ryoga by using and disguising his female form to create "Yoiko" and get his own back.
Ranma reveals himself as Yoiko to Ryoga shortly after Ryoga finishes making some tea for Akane. Obviously confused at who Yoiko is, Yoiko breaks into a flood of tears that her "brother" doesn't remember her. As Ryoga sits back in shock, Yoiko adds that it's no surprise since he hardly ever comes home anymore. Remembering how he didn't know Shirokuro had had puppies, Ryoga blindly deduces that him having a forgotten younger sister isn't too far fetched (although this ruins Ryoga's plans of being alone with Akane).
Yoiko then goes with Ryoga back to the room where Akane is still playing with the puppies. Akane immediately notices the similarity between Yoiko and Ranma's female form, but dismisses this idea given Ryoga's position in the whole situation. Ryoga then decides to take Akane up to his room, and instructs Yoiko not to get in the way, which Yoiko happily agrees to.
Inside his room, Ryoga tries to confide his feelings to Akane. Unfortunately, Yoiko intervenes by making it look like Ryoga's talking about his feelings toward his sister. Ryoga swiftly throws Yoiko out of his room and tries to continue being alone with Akane. However, Yoiko soon returns when Akane mentions that Ryoga and Yoiko don't look much alike, prompting Yoiko to show they both prominent fangs, thus proving they're related. Yet again Ryoga throws Yoiko out of his room and decides to show Akane a video of Shirokuro as a puppy in order to set the right mood.
As the video plays, Ryoga anxiously waits for Akane to pick up a cracker so that he can romantically try reaching for the same one and touch her hand. But this time Yoiko and Shirokuro appear and begin trying to grab a cracker. Infuriated, Ryoga drags Yoiko out of the room so that he can have a talk with her. This soon backfires, however, as Yoiko begins crying at her brother seeing another girl as more important than her, especially when she's been so lonely and waiting for him to return. Yoiko then lashes out at Ryoga, ultimately slamming him into a wall in the hope of rending Ryoga unconscious. This backfires as well as Ryoga embraces his sister and begs for forgiveness from her.
Ryoga then gives in and takes Yoiko back to his room with Akane and Shirokuro so that she won't be lonely. Yoiko decides that while she's got Ryoga hooked she might as well keep reeling him in and teases Ryoga about flirting with Akane, to which Ryoga responds by poking Yoiko on the forehead whilst telling her not to tease his older brother. As Yoiko sits in the pile of souvenirs that fell on her (Ryoga's brute strength knocked Yoiko a wall), Akane looks at Yoiko and thinks again that she looks very similar to Ranma.
Some time passes and Ranma begins tiring at her disguise. When Ryoga asks Yoiko if she's having fun, Ranma is so tired that he gives a very out-of-character response. This angers Ryoga who begins hitting Yoiko for giving such an unladylike response before passing his reaction as being a strict big brother. This scene convinces Akane that Yoiko is just too stupid and therefore has to be Ranma in disguise.
Akane decides to test her theory by boiling some water for tea, only to pretend to trip up and have the water fall towards Yoiko. Unfortunately for Akane, Ryoga intervenes by pushing Yoiko into the wall so that the water only lands on him. Ranma decides she's had enough by this point and attempts to make her escape through the window but is spotted by Ryoga who demands to know where she's going. Yoiko replies that she's going for a walk, but, knowing their family's non-existent sense of direction, Ryoga refuses to let her go alone, so Ryoga, Akane and Shirokuro go with Yoiko for a walk (carrying the puppies as they go).
Whilst they walk, Ryoga refuses to let go of Yoiko's hand, but this doesn't prevent Yoiko from escaping by switching herself with a Dogū. Yoiko hides away while Ryoga desperately searches for her, unfortunately, a cat appears and Ranma's Ailurophobia sets in, causing her to flee via a nearby fence. The others soon spot Yoiko and Ryoga gives chase. Ryoga tries to call to Yoiko, but she outright ignores him. This prompts Ryoga to throw a pebble to get her attention, but when that doesn't seem to work either, Ryoga throws increasingly larger objects at his sister to get her attention.
Ultimately Ryoga decides to throw a brick pillar at Yoiko, which she can't outrun. Ryoga then searches the rubble for his sister, but can't find as Yoiko managed to hide away in a nearby statue. Once Ryoga leaves, Yoiko stumbles around with a walking stick, determined to get home, when she comes across one of Shirokuro's puppies and decides that it must be lost. Meanwhile, Ryoga is distraught that he may never see his sister for years given their lack of sense of direction. Just then Shirokuro sees Yoiko with her puppy and rushes over, followed by an overjoyed Ryoga who almost crushes Yoiko with his hug.
Once they return the puppies home, Akane decides she'd best leave, although Yoiko doesn't want her to. Ryoga then places handcuffs on them so that they can never be separated again when the phone rings. Ryoga rushes over (dragging Yoiko along with him) and is happily surprised when he realizes his father is on the other end. Ryoga tells his father that him and Yoiko are doing fine, but obviously Ryoga's father has no memory of "Yoiko". Having had enough of Ryoga, Ranma blows her disguise by removing her fangs, causing Ryoga to finally recognize Ranma. Extremely angered, Ryoga crushes the phone before beating up Ranma and allowing her and Akane to return to the Tendo Dojo.
Being an alias, Yoiko posses the same skills that Ranma does at the point of her appearance. Ranma generally seems to hold back using any techniques so that he could maintain his "good sister" guise.
The only time which Ranma breaks this mind set is when she pretends to become upset at Ryoga for viewing Akane as more important than his own lonely sister, where she hits Ryoga multiple times and ends up causing the pair of them to slam into a nearby wall. It's very likely that Ranma was using her Kachu Tenshin Amaguriken technique in the hope of rendering Ryoga unconscious, similar to when they last fought.
In order to be perceived as a good "sister", Yoiko initially showed no hatred towards Ryoga. The only time this changed before Ranma was tiring of her disguise was when Yoiko became upset (and possibly slightly jealous) at how Ryoga was seemingly treating Akane as more important than her, especially given how Yoiko claimed to have become lonely when her brother almost never came home anymore. In a similar fashion, Ryoga showed nothing but support to his apparent younger sister. Ryoga's support towards Yoiko did increase after she explained how lonely she became and made Ryoga become extremely protective of her so that the loneliness she claimed to have felt wouldn't return. Ultimately of course Ryoga completely changes his feelings towards "Yoiko" when she reveals herself as Ranma, prompting Ryoga to furiously beat up Ranma for her deception.
- Despite being exclusive to the manga, Ranma can be seen in a Yoiko Hibiki guise in the Earth Orchestra opening theme, possibly indicating that the Ryoga Goes Home Arc was considered for an anime adaptation at some point.
- Welcome home, big brother! - Yoiko welcoming Ryoga home.
- That's right, big brother! I'm here for you! - Yoiko interrupting Ryoga trying to confess to Akane, before getting thrown out of the room.
- I'm sorry, big brother! You were flirting with her, weren't you? - Yoiko teasing Ryoga after he allows her to join him and Akane.
- Like fun I'm having fun. - Yoiko's response when Ryoga asks her if she's having fun.
- Take a look, dope... See? - Ranma removing her fangs and revealing her true identity to Ryoga, shortly before he beats her up.