Generally, Kotonoha Katsura is an intelligent, bookish, well-educated, girly, polite and gentle young lady with a reserved character.

Kotonoha's role in the anime is largely the same, becoming Makoto's girlfriend, only until at the end of episode 3 when Makoto quickly begins to tire of her, as she is unwilling to do anything intimate with him, and gets closer to Sekai. She is later ignored by him and desperately tries to get his attention but is bullied and  then supposedly raped by Taisuke. Her Yandere nature soon appears and she pretends to be Makoto's girlfriend and "talks" with him on the phone. He eventually takes her back once he realizes how poorly he treated her and after none of the other girls are willing to talk to him anymore but after a date with her, he breaks up with Sekai when she shows up at his place going as far as encouraging abortion as Sekai is pregnant of Makoto, This ends up sealing his fate as Kotonoha, with the aid of her fathers connections recommends a good doctor for Sekai to get an abortion. Too add insult to injury Kotonoha makes out with Makoto in front of Sekai and lets her know that she doesn't care that Makoto cheated on her and that is now willing to do anything sexual so he stay with her. Later Sekai asked Makoto to meet at his place to discuss about the relationship yet she ended up killing Makoto after seeing the discarded dinner which she prepared the evening before. Sekai sent a text message with few pages of empty lines and a last word "farewell" before stabbing Makoto to death. She then fled the scene, leaving Makoto's lifeless body lying on the floor to be discovered by Kotonoha shortly after. This causes her to go even further insane, and she decapitates Makoto's head and puts it in a bag she brought with her, going on to text Sekai using his cellphone to meet with her on the roof. She speaks to Sekai and reveals his decapitated head before killing her. Finally she sails away on a boat with "Makoto" and whispers now they can finally be together.