I think he's supposed to be in here
http://www.mangago.zone/read-manga/koicha_no_osahou_tea_for_two/
but I haven't actually read it to make sure.
He is in that one but he's a little boy. It's not a very big part but he's pretty cute just the same.
He said junpei not shunpei
Same kid though. Here he is again: http://www.mangago.zone/read-manga/koicha_no_osahou_tea_for_two/mf/v03/c002/13/
It's just the translation
I think he is Shunpei while looking at baka updates it says
https://www.mangaupdates.com/series.html?id=23448
Note: Shunpei from Koi Cha no Osahou appears in this story as the main character's best friend.
What about shunpei? His story ? (づ ̄ ³ ̄)づ