When a former senpai comes back into his life after 11 years, Hoshino is surprised. He is confused and slightly terrified after said senpai finds out that Hoshino has kept and treasured a pen that he'd given to Hoshino many years ago.
Yozora no Sumikko de is a completed manga by Hayakawa Nojiko, first published in 2013. It blends boys' love, drama and slice of life. You can read all 11 available chapters of Yozora no Sumikko de online for free on MangaPulse; the newest is Chapter 9.2, added 2018-02-09. The series is finished, so you can read it from start to end in one go.