it can take place in the HakuĊki setting with female okita paired with any of the other Shinsengumi leaders from the game or anime

or in the nasuverse with any of the major characters summoning sakura saber as a servant or it can crossover female okita or sakura saber with any other series

universes i would like to see crossover

naruto

bleach

samurai x

Peacemaker Kurogane

Bakumatsu Kikansetsu Irohanihoheto

Ghost Sweeper Mikami,

ginatama

sengoku rance

Moeyo Ken

High School DxD

tsubasa chronicle

harry potter

profile here wiki/Sakura_Saber

Mordred calls Saber father and Sakura Saber mother due to their similar appearance.