Why is this tagged as official art?

I don't know, but you can edit tags yourself, you know.

Anyway, this is from an ecchi work containing Evangelion and Gunbuster. It also contains, or is used for, an ecchi NGE calender.

This is from the "Stripping Instrumentality Project", an official game by Gainax as part of their "Eva and Good Friends" mahjong series.

Oh, then maybe the calender and book also featuring Gunbuster was just a spin-off of that.

it looks like her arm is growing from her stomach