Blue Box, Vol. 01 by Kouji Miura

Taiki Inomata is a passionate badminton player, striving to reach the national championships. His admiration for Chinatsu Kano, a dedicated member of the girls' basketball team, grows as he watches her train. Unexpected events bring them closer, causing sports to take a backseat to their budding relationship. Despite his doubts, Taiki musters up the courage to encourage Chinatsu to never give up on her dreams. Will this bold declaration lead to the start of their high school romance?