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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).