Shun Matsuoka maintains childhood friendships with Kaname Tsukahara, Yuuki Asaba, and Yuuta Asaba into high school, where transfer student Chizuru Tachibana joins their circle. He shares especially close ties with Yuuta, participating alongside him in both their current tea ceremony club and former middle school kendo club. His family includes two older sisters and a younger brother, Fuyuki Matsuoka, whose abrasive independence contrasts with Shun's nature and occasionally causes Shun concern over Fuyuki's social behavior.

Physically, Shun possesses light maroon hair and delicate features, initially worn long enough to prompt frequent misidentification as a girl—notably by Chizuru and others upon first encounters. After Chizuru and the Asaba twins cut his hair short, it develops a poofy texture when wet from rain, amplifying his gentle demeanor's feminine impression.

Sensitive and emotionally open, Shun often uses *keigo* honorifics and mediates friend conflicts, contributing a cheerful, calming "iyashikei" presence. However, he exhibits romantic naivety: he reacts with shocked confusion to a confession from another school's student and remains oblivious to classmate Masaki Sato's persistent feelings despite peers recognizing her affection. His development involves navigating complex dynamics like Masaki's affection intersecting with Chizuru's feelings, where his limited awareness leaves him largely passive despite catalyzing tensions. Childhood emotionality, like frequent crying when teased by Kaname, matured into high school empathy for others. Interests include baking, reading, and television dramas, distinguishing him from peer group stereotypes.