Koganei Kyoudai no Kyuusoku
小金井兄妹の休息 · こがねい きょうだい の きゅうそく
est. Rough estimate based on volume count, reprints and magazine — not an official figure
Overview
An otaku-minded older brother Arata and his gyaru younger sister Hana live together in the suburbs. The two of them spend this summer vacation they never expected to have as they please. (Source: Web Action, translated)
Source: AniList
External databases: AniList
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections