The Girl I Saved on the Train Turned Out to Be My Childhood Friend, Vol. 1 (manga)

When Ryou Takamori confronts a groper on the train, it turns outhe's come to the rescue of his estranged childhood friend, Hina Fushimi. The two drifted apart in middle school as the social gap between ever-popular beauty Hina and plain loner Ryou widened—but this incident might be the catalyst Hina's been waiting for to rekindle their friendship. And she's got her fingers crossed that it'll spark something more…if only Ryou would get a clue!

Volume 1 of The Girl I Saved on the Train Turned Out to Be My Childhood Friend manga series by Fly Kennoji.