![1boy 1girl ahoge alternate_costume bangs bare_shoulders black_bow blonde_hair blush bow breasts cellphone cellphone_picture eyebrows_visible_through_hair fate/grand_order fate_(series) fujimaru_ritsuka_(male) green_eyes hair_bow highres holding holding_phone jitome koha-ace looking_to_the_side medium_breasts mitsurugi_sugar okita_souji_(fate) okita_souji_(fate)_(all) phone ribbed_sweater screen sidelocks sleeping smartphone sweater translation_request upper_body rating:s score:18 post #3763004](/cdn_image/preview/50/3f/503f51a0da855e3cf9103a00770339b4.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).