Yukiya-kun no Ongaeshi

University student Shunpei is so dedicated to helping others and volunteering that he's earned the nickname "The All-Out College Student." His passion is so intense that people can’t help but wonder—why does he go that far? One day, while taking a break between lectures, Shunpei is suddenly kissed by a mysterious, handsome young man!? The stranger, Yukiya, claims that Shunpei once saved him in the past—and without hesitation, he moves right into Shunpei’s apartment…!?

(Source: Taiyohtosho, translated)

Note: Includes an extra.