Kimi ga Boku no Mannaka
君が僕のまんなか · きみ が ぼく の まんなか
est. Rough estimate based on volume count, reprints and magazine — not an official figure
Overview
Steady and caring Yuzuki and clumsy and spoiled Miumi are unrelated sisters. They've always gotten along like best friends, but one day Yuzuki meets someone she's interested in. Yuzuki is steadily getting closer to him and is filled with happiness. But Miumi can't help but worry... (Source: Shogakukan, translated) Note: Includes two extra chapters.
Source: AniList
External databases: MADB · AniList
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