![2girls :o @_@ bangs black_bow black_scarf blonde_hair blue_cardigan blue_sailor_collar blush book bookshelf bow brown_eyes cardigan chair chalice closed_mouth comic commentary_request directional_arrow eraser ereshkigal_(fate/grand_order) eyebrows_visible_through_hair fate/grand_order fate_(series) hair_between_eyes hair_bow holding holding_pencil holy_grail_(fate) indoors koha-ace long_hair long_sleeves multiple_girls neckerchief nose_blush notice_lines okita_souji_(fate) okita_souji_(fate)_(all) on_chair open_cardigan open_clothes parted_bangs parted_lips pencil red_bow red_eyes red_neckwear rioshi sailor_collar scarf school_uniform serafuku shirt sitting sleeves_past_wrists smile sweat table tile_floor tiles translated two_side_up very_long_hair visible_air wavy_mouth white_shirt rating:s score:5 post #3713603](/cdn_image/preview/92/a7/92a7227f4951c879943de97b7c3aad2d.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).