Kasumi is an individual who is often found lost in thoughts. Unless someone calls her out, she can think about something for hours. It's not easy to approach her if she isn't familiar enough with you. She's not very talkactive around people unless she trusts them. She's often accompanied by a rather melancholic looking expression on her face, although she truly enjoys smiling and laughing. Once she has set her goal on something, it's hard to make her give up. It's often the case that she wants to impress someone by being determined. She is a fast learner, thanks to her perceptive skills she quickly understands concepts. She improves those skills by observing other people. She is easily embarrassed when someone points out her mistakes. In said state she performs poorly in comparison to how she usually would and acts without thinking.

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Currently, she attends True Cross Academy and its exorcist cram school as a spy for a secret underground exorcist organization. She was forced to join and taken away from her family, who made a pact with them when their life was in danger, which happened during the time Kasumi's mother was pregnant with her. The reason why exactly they had to make this pact is unknown to her.

Since her birth she has been able to see demons and used to be afraid of them as a child, but people brushed it off as her imagination whenever she mentioned it.

Up until junior high, she has been living a somewhat peaceful life. But once she enrolled, her grades and social life went down the drain and ended up being a cast-out. For a while she was all alone until she met an upperclassman who was just as lonely as her and they ended up developing a close bond. Kasumi really looked up to her and was gifted an accessory by her, which she is still wearing to this day. But ever since she was taken away during her second year of junior high, she hasn't seen her.

After joining the underground organization, she went through harsh training for an entire year before enrolling at True Cross Academy. It was during this time that she received her familiar, Jin, who is able to transform into various weapons. Her mission is to observe a certain student and make daily reports.