 If you liked
NHK ni Youkoso!
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 ...then you might like
Rozen Maiden (2008)
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The main male protagonist is a hikkikomori, and the story has some focus on his recovery with the help of the female protagonist(s). Welcome to the NHK is a more realistic story with a heavy focus on hikkikomori issues, whereas Rozen Maiden is a fantasy involving living dolls, but the male protags' struggles in both series revolve around their status as shut-ins.