My Youth Romantic Comedy Is Wrong, As I Expected, Vol. 4 (light novel) — Wataru Watari

SUMMER CAMP IS A MINEFIELD FOR A LONER...
Ahh, summer break. No school, no responsibilities, and no friends to pass the time with -- until Miss Hiratsuka drafts the Service Club (plus a few normies) into volunteering to supervise an elementary school camping trip. But Hachiman has a knack for sticking to the sidelines and is prepared to survive this awkward outing with as little conflict as possible -- until he meets a little girl who's already started down the path of loner-dom herself.