Ao no Flag
Alternative : 蓝色的旗帜 ; 青のフラッグ ; Ao no furaggu ; Blue Flag

Author(s) : Kaito,

Status : Ongoing

Genres : Drama, Romance, School life, Shounen, Slice of life.

Ao no Flag manga summary:

The "youth pure love" story begins when three students in their third and final year of high school meet during a time when they are worried about paths for their futures. Waiting for them are sweet, painful, and heartrending days.

https://manganelo.com/manga/ao_no_flag

https://mangaplus.shueisha.co.jp/titles/100043