Boku no Suki na Hito ga Suki na Hito

Sora Akizuki, a second-year high school boy, confesses his feelings for the kouhai girl Miya Fuwa, but she rejects him because she "likes someone else." The person she likes is... Asahi Suzukaze, the head of the mysterious "Clinical Trial Club." Sora joins the club, only to find out that Asahi also has someone she already likes. He is a boy who once saved Asahi, who was seriously ill, by helping her get through a "clinical trial," so she calls him "the prince of clinical trials." But it turns out that boy is Sora, who was a mischievous elementary school kid at the time.........?

This is a high-tension "clinical trial" romantic comedy with a complex intersection of love interests!

(Source: Young Animal, translated)