neet_de_otaku_na_kunoichi_to_naze_ka_dousei_hajimemashita
Webmanga by koyuki (kotatsu358).
A salaryman, Atsumi Tsukasa, lives with a kunoichi, Ideura Shizuri, that protects him from demons summoned by an ancient family curse. However, when not slaying monsters she spends her time as a layabout game otaku.