Happy Happia!

[MangaDex]

 

[BakedBanana]

Box girl box looks like a sugar cube in the cover art:

 

[sarusa]

This manga should probably be 'Happy Happier!' in English, but the raws are very insistent that it's 'Happi Happia!' in Englsh, so that's what we're going with. At one point the raws even call it 'Happy Happy Peer', so... at that point, whatevah! This is not a manga we need to think too hard about.