The Girl I Saved on the Train Turned Out to Be My Childhood Friend, Vol. 3 (light novel) - GIRL SAVED ON TRAIN CHILDHOOD FRIEND LN SC

There's only one month left until the July field trip, and Hina Fushimi is
still making
enthusiastic advances on Ryou Takamori. But when a girl named Ai
Himejima, another
one of Ryou's childhood friends, transfers to their high
school, Ryou and Hina's
relationship hits a snag. Faced with a rival in love,
Hina redoubles her efforts to win
Ryou over by resorting to even bolder feats
of flirtation. Ryou, meanwhile, continues to
act completely
oblivious!