Junichi Katsuragi (桂木淳一 Katsuragi Junichi ) is a senior to Sentarou, who idolizes him and calls him a Brother Jun. He comes from a wealthy family.
Junichi plays trumpet in the jazz band. According to Sentarou, he's good at fighting and is popular among the girls at school.
He is asked to run a cafe own by his family called "Shirayuri", but he rejects and decides to study in a university in Tokyo.
During his campus life, he participates in a political club and several student movements, which makes him feel distressed and eventually leads to the suspension by the school. His parents are irritated and kick him out of the family.
Homeless and penniless, he is luckily found out by Ritsuko's father and later lives at the Mukae's house for a while. During that period of time, he is addicted to alcohol, smokes, and tranquilizer heavily, and also suffers from mental illness.
During one Christmas night, he performs jazz at an American soldiers' bar, whose performance is so outstanding that attracts Yurika's attention. She falls in love with him soon, and he even gives her a kiss in the basement after they meet for the second time.
In the first place, he wants to reject Yurika's affection since he doesn't want anyone to sacrifice for him, a worthless man abandoned by the society as he considers himself. Nonetheless, Yurika still wants to help him out of his trouble due to her unchangeable love for him, which encourages him and makes him fall in love with this woman too.
One day, he receives the letter sends by his friend, who offers him a job as a journalist in Tokyo. He then has to bid farewell to Yurika, but he eventually changes his mind by taking her on the journey together.
In the anime, it's revealed that Yurika is pregnant for six months at the hospital, and Junichi hopes the kid is a girl. In the manga, the photo of their children is shown, they are a pair of identical twin baby girls.