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The Girl I Saved on the Train Turned Out to be My Childhood Friend

Chikan Saresou ni Natteiru S-kyuu Bishoujo wo Tasuketara Tonari no Seki no Osananajimi datta
痴漢されそうになっているS級美少女を助けたら隣の席の幼馴染だった
성추행당할 뻔한 S급 미소녀를 구해주고 보니 옆자리 소꿉친구였다
Я спас красивую девушку от насильника, а она оказалась моей подругой детства

Adaptation

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When Ryou Takamori confronts a groper on the train, it turns out he’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! 

(Source: Yen Press)