Osana Najimi

This girl is planned as ''' the first rival for Senpai's affections. She will be used as a tutorial in the beginning of the game.'''

Since her AI is incomplete, Osana Najimi cannot be interacted with (include killing, talking, etc.). Yet, she'll still confess her feelings to Senpai on Friday, resulting in the "Heartbroken" scene. During gameplay, you can find her standing underneath the first cherry blossom tree on the left row, close to the school gates.

She is not active yet because YandereDev wants to give a different character model to make her more unique, but her character model is not compatible with all of the animators that were made for the other female skeleton that the rest of the female have. Osana can't be put into the game unless a character rigger makes a control rig for her, and an animator uses this rig to create a full set of animations for her, or YandereDev gives her the same character model and animation as all of the other female students.

The downside of giving her the same character model as all the other female students is that she will look like a clone of Yandere-chan, but with different eyes, hair, and stockings. So far, YandereDev can't find anyone to get it done.

Appearance
Osana Najimi is an extremely short girl and is actually the shortest character in the game. She has ruddy cheeks in a blush, a soft smile, orange eyes, and pale skin. Her ginger hair is worn in two slightly curling pigtails. To keep her hair up, she wears ruffled pink and white polka-dotted scrunchies and a purple ribbon. She wears the default female school uniform unless customized, and black shoes, although with white Kogal-style leg warmers.

She is probably getting an update with long twin tails, the same pink scrunchies with white polka dots, and salmon socks with white polka dots. But this hasn't been confirmed.

Scenes
In the original intro to the game when you run into Senpai, she can be seen talking to Senpai and acting tsundere towards him.

You can see that intro on YandereDev's YouTube channel.

She also appears in the spinoff game Yandere Clicker. Her face was used for the "Imouto" option, described as "A kawaii Imouto who will stab Senpai for you." However, she is not Senpai's little sister and should not be mistaken as such.

In the April 3rd build, the photographs folder had a lot of pictures of her in different positions. You cannot see her move from her spot in the actual game. However, in one update, you can press spacebar to see her do some animations.

In the second intro added in the August 15th build, Osana is mentioned by Info-chan as she requests that Yandere-chan murders the girl. Info-chan expresses that she wants Yandere-chan to "make her suffer". It is unknown what Info-chan has against Osana and it is never revealed whether Info-chan is still just a curious journalist who wants despair to boost her newspaper like in the first opening, or if there's something else.

Personality
Osana Najimi was originally tsundere, which is a person that is very sweet, kind, and cute, but projects a hostile attitude to those around her, often only towards their love interest. It's not very likely that Senpai would know about her crush on him, as she repeatedly insults him. Deep down however, she is very considerate. In the original intro, she is shown walking Senpai to school.

The characterization might have changed. On this page at the very bottom, YandereDev says that Osana Najimi is the tsundere childhood best friend of Senpai. The page was right about the nurse, as confirmed on the Nurse's page which would suggest that some of the info might still be true, despite the fact that the page was extremely ancient. Yet even so, on the Rivals page, in the Trivia section you will notice that the page might've been wrong about the Imouto, another rival, being innocent and sweet. Therefore, because of there was a change to the Imouto's personality, the same could've been done to Osana. This is even more implied by the second intro, which shows nothing about what Osana is really like. The only thing we know now is that Osana likes Senpai, is a target of Info-chan and Yandere-chan, and believes in the myth about the cherry tree behind the school.

Senpai
They were childhood friends in the first intro. Osana has a crush on him, although he does not seem to be aware of it. The first opening shows Osana and Senpai together, and even walking to school with each other. In the second intro on it's own there is no information about what their relationship now is. Osana still has a crush on him though and will still confess to him. As with all rivals, as mentioned here, Senpai will be on good terms with Osana and will not accuse her of bad doings if she's bloody. If Osana is in deep trouble with tons of evidence against her, then Senpai will not be able to support her any longer.

Yandere-chan
Osana Najimi is a target of Yandere-chan because she is a rival to Senpai's affections. In the first intro Yandere-chan qualms about killing others. She simply wanted a love life and Osana was in the way, but Info-chan, a glory-hungry journalist, convinces Yandere-chan to kill Osana. In the next intro Yandere-chan already wanted Osana out of the way, by any means necessary. Info-chan just encouraged her more and gave her some info.

Osana, like all the other rivals, will not know that Yandere-chan is a rival.

Info-chan
In the first opening Info-chan didn't hold anything truly personal against Osana. Still, it is now known that back then Info-chan was the main antagonist who was going to be a rival for your Senpai, as seen on Info-chan's page. It is also known that in the original intro Info-chan wanted some terrible events to unfold at Akademi High to boost her newspaper sales.

In the second intro it is not stated why Info-chan is going against Osana. Info-chan simply wants Osana to suffer, though anything about being a journalist is never stated.

Trivia

 * Osana Najimi's name is a pun on "osananajimi," a common trope in the romance genre which means 'Childhood Friend' in English. This is a reference to her relationship with Senpai, who shares with her a close bond due to knowing her since they were children.
 * In the Challenges menu, there's a silhouette of a girl victim that seems to resemble Osana.Challlmenu_-_osana.jpg
 * She is the first official rival to be introduced so far during the build era.
 * She makes a small cameo in the April Fools'trailer.
 * You can buy Osana Najimi's 3D model on the Unity Asset store, and her model is named Satomi Makise.
 * Currently, except the text message intro, Info-chan won't give you information about her due to not recognizing her placeholder model.
 * She is the first Tsundere character to be introduced by YandereDev, the second being Tsundere-chan from Kuudere Simulator.
 * If you press spacebar, Osana's idle animation will change. She will do different animations.
 * It is implied on Twitter that Osana's birthday will be in January, probably the 1st.