User blog comment:B214/Volume 22 spoilers/@comment-175.110.173.31-20160829100254/@comment-9595671-20160829113606

Recall how when she slashes Durandal it can sometimes make an energy wave? Cross Crisis is this when she uses both Durandal and Excalibur to do it in a cross shaped fashion, taking advantage of how she does better at using two swords at once.

The said fanfic is a story about Xenovia and Irina before meet with Issei, I haven't read it myself because I'm currently catching up on some other fanfics, so I don't know anymore about it just yet.