Fate/ikustella summary:

For unknown reasons, the three versions of Hakuno have turned into babies in an alternate timeline. Archimedes, still trying to reset the Moon Cell, is shocked at the situation and cannot make any sense of it. The two Hakuno with Nero and Tamamo, Mind and Soul, are one child, the male Hakuno, while the Body Hakuno with Altera is the female Hakuno.
Meant for those who have beaten the Fate/Extella game.