Shiraoka Ryuuji

Ryuji Shiraoka was a college classmate of Kohei and Tsumugi.
He was originally a friend of Tsumugi's and got acquainted with Kohei through that connection.
At best, he is cheerful and open-minded; at worst, he is thoughtless and frivolous.
She is not a bad person at heart and has many friends, both male and female.
Although he and Tsumugi were not boyfriend and girlfriend for a long time, they had been in a "deep relationship" until he started dating Kohei.