![1girl bangs blue_sailor_collar blue_shirt blush bow box breasts brown_bow brown_hair commentary_request eyebrows_visible_through_hair fate/grand_order fate_(series) gift gift_box grey_eyes grey_sweater hair_between_eyes hair_bow hakuda_tofu hand_up heart koha-ace long_sleeves okita_souji_(fate) okita_souji_(fate)_(all) parted_lips red_neckwear sailor_collar school_uniform serafuku shirt sleeves_past_wrists small_breasts solo sweater translation_request upper_body rating:s score:6 post #3780996](/cdn_image/preview/31/74/317464225309af3e2606322b4fda9547.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).