Kirio Karasuma is a central antagonist in Kamichama Karin, serving as a primary adversary to the protagonist, Karin Hanazono, and her allies. He is a student at Sakuragaoka Academy, where he holds the position of student body president. Karin frequently refers to him by nicknames such as Glasses Guy, Mr. Glasses Man, or Four-eyes-san, due to his distinctive eyewear.

Kirio is the son of Kirihiko Karasuma and has a twin sister named Kirika, with whom he shares a strong familial bond. His family is also connected to Himeka, whom he regards as another sister. Both Kirio and Kirika have lost their parents. His family name, Karasuma, is shared with his father and sister, following a theme of similar-sounding names.

In terms of personality, Kirio is largely defined by his role as a testing and antagonistic force against the main characters. He is known for confronting Karin and Kazune Kujyou outside of school grounds to challenge them. Despite his menacing role, the anime adaptation portrays him with a recurring comedic trait, often leaving a scene or revealing his plans prematurely before he can claim victory, while mistakenly believing his opponents are aware of his schemes. An example of his disruptive role in the story includes walking in on Karin and Kazune in a compromising situation, highlighting his function as an obstacle.

Kirio possesses a ring that grants him the powers of the god Ares. This power is similar in nature to that of his sister, Kirika. He uses this ring to pursue Himeka for reasons that are initially unknown, prompting Karin and Kazune to vow to protect her. His actions are ultimately tied to the larger plans of his father, Kirihiko. Over the course of the story, Kirio undergoes significant development. His own ring is eventually destroyed by Kazune. Following this, he becomes possessed by the power of Zeus's ring. In the end, he is healed and saved by Karin and Kazune, marking a resolution to his antagonistic role.