An 18-year old honors student. She has both the brains and beauty and is said to be a dream girl of many young men, making her popular in school. Up until the last two days of the game, Io is constantly apologising and always compromises, agrees with others and never forces her own viewpoint on others out of fear of being hated. This frustrates Airi several times because she thinks that Io is very superficial, and when she tells Io to say what’s on her mind, Io realises that she hardly even has any opinions of her own. She pauses a lot when talking and Yamato chews her on her non-confrontational policy. At the last two days, she eventually found her resolve and decided to be more courageous on expressing her own feelings. She seems to develop a crush on the Protagonist.
Her death clip shows her dying when she couldn't handle Lugh's power. To prevent her death clip, you need to fulfil the two requirements: She needs to have a high enough Fate link and you must immediately talk to her after she runs away.
In the anime series, Hibiki manages to avert her death clip and return her to normal. Io's initial demon is Ogre and later she also obtains Pixie and Goddess Kikuri-Hime, and Lugh after her possession. She died from being consumed by the Void along with Daichi. She is revived once the world is restored to before the invasion and is invited to go home together by Hibiki, which she accepted as she has vague feelings of knowing them.