@OtakuD50
Huge Spoilers for Higanjima’s third series.
They don’t have the time to. Yuki barely does anything in the second series and is separated from Akira for most of it. Then in the third, she suddenly comes back at some point and it’s revealed she and Nishiyama became vampires, with her specifically becoming a gigantic demon, while Nishiyama went mad and ended up becoming her demon master. After a long fight, Akira ends up killing both.