I knew Kosaki wanted to be there for Chitoge. I said they needed to see each other, even back when Raku and Kosaki visited New York trying to meet her.
So that they could support each other, even in this situation. She needs to find her best friend, and give her the push she needs to keep going, despite how impossible it may seem from her perspective.
Also, Tsugumi rocking new skills Yoko Honda taught her, I wager. Surpassing the master, love to see it.