Misaki is a university junior, studying agriculture. He works with Professor Tsujimura in the labs, doing research. He's very reserved and soft-spoken, initially treating Arikawa coldly after he embarrasses him in public, but gradually warms up to him. He's also clumsy and easily flustered. His appearance is feminine, and it's common knowledge at his university that he was sexually harassed by a male student because of his looks.
His parents died in an accident when he was a teenager, so he moved in with his grandfather, and was mentored and tutored by a student of his, Kawabata. It was with them that he developed an interest in botany. His grandfather died from a stroke, however, leaving him solely in Kawabata's care. Kawabata instigated a romantic relationship with him, and Misaki fell for him; it was from him that he got his flower necklace. But Kawabata eventually decided he had to end it and got a girlfriend. After that, he started treating Misaki possessively, interfering with his life and interrogating him about his relationships, and taunting him about his sexuality.
As a result Misaki is afraid of Kawabata, and of his feelings for Arikawa (he's specifically scared of losing him to a woman). He's shown wishing he was a girl in a couple of scenes, so he could have a relationship with a man. He and Arikawa get together anyway, though, in Chapter 9, after Arikawa confesses his feelings.