Yuki Yoshida (吉田 由紀 Yoshida Yuki) was the childhood friend and ex-boyfriend of Mafuyu who died from an apparent suicide roughly half a year prior to the start of the series. He played guitar in a band with Hiiragi and Shizusumi.
Similar to Hiiragi, Yuki has long goldenrod dyed hair at the top with short light brown hair at the bottom and hazelnut eyes, as well as a sea-green colored uniform along with black jeans. He wears three-ringed piercings in his left ear.
Yuki likes showing off and is a dominant and charismatic person. However, he is very caring and affectionate towards Mafuyu, as they are mostly seen being together. Yuki is also observant around Mafuyu.
Yuki is mentioned by other people, mostly in relation to the rumors of him going out with Mafuyu in middle school. Another rumor is that the reason for his suicide had something to do with Mafuyu.
From Japanese 由 (yu) meaning "reason, cause" combined with 紀 (ki) meaning "chronicle".