The Usual tactics against Spirits and Quasi spirits is the Time Blitz with Time acceleration, firstly, she is able to time accelerate to a point where 500 Opponents with a view from the sky can't even see her moving and 1000 have trouble (yea she is against 1500 Quasi-Spirits)

Those point aside let's talk about Some Kurumi's tactics as win-con: It's shown earlier in the anime and or LN that the decapited Kurumi is a main one due to her use of Zaphkiel earlier. The new main then appears from a wall after.

Kurumi smiled as she touched her hand with her finger. It seems she had exchanged places with her clone. It cannot be, do you think that something like this would be enough to kill me?' 'Kehehe, your greeting style is as unrefined as ever.' At the same time, the fallen Kurumi's body was absorbed by the shadows. Then, the shadow on the walls of the building began to widen, revealing Kurumi's crooked smile. The brainless body continued to convulse as it created a red puddle on the floor. It was clear that there was no hope, yet Shidou continued to run towards Kurumi. At the same time, Kurumi's body fell to the ground like a lifeless puppet. Shidou screamed loudly as he fell to the ground. At this moment, Shidou's brain finally registered what had happened. Then, the place where Kurumi's brain was supposed to be began to spray out blood like a fountain, staining Shidou red. It was sudden, and Shidou didn't understand what had happen in that moment, aside from a low sound. The Kurumi, who had been conversing with Shidou, had her head thrown into the sky. No in both the anime and LN Shido talks with the main Kurumi who holds Zaphkiel who then get's decapitated from behind by Mana.

Quotes of ancestor darkest dungeon