User blog comment:Xilinoc/Ch 649 - The Theatre Suicide SCENE 3/@comment-1248963-20151029173316/@comment-5398287-20151029230657

Honestly, I figure Lille was only kept alive to extend the fight so 1. Shunsui could enter a flashback explaining all the mysterious shit he's said over the past couple chapters, and 2. so Nanao can intervene somehow and get her time to shine. I could be wrong, but from a purely story-wise point of view that makes sense to me.