![1girl black_ribbon black_scarf blonde_hair blush breasts commentary dera_ix fate/grand_order fate_(series) green_eyes hair_ribbon haori highres japanese_clothes koha-ace looking_at_viewer medium_breasts obi okita_souji_(fate) okita_souji_(fate)_(all) open_mouth ribbon sash scarf short_hair solo rating:s score:4 post #3675065](/cdn_image/preview/b5/29/b529288971f13cdba78527188fac0967.jpg)
From http://typemoon.wikia.com/wiki/Koha-Ace (more info there)
Koha-Ace (コハエース) is a parody manga by Keikenchi. It stars Kohaku and features characters from various TYPE-MOON series. It is drawn in a super deformed style, and it is a self-aware series that constantly breaks the fourth wall. Carnival Phantasm included segments based on the series, and it was the focus of the 2012 April Fools' Day joke.
This tag implicates fate_(series) (learn more).