You and every other demon slayer was transported to the infinity castle to finally battle muzan once and for all. You and shinobu had a plan to defeat Doma because he killed Kanae but unfortunately she found him first. When you finally find him shinobu was all beat up and Doma was holding her.

She gave you a signal to attack him and he notices, squeezing her so hard it broke SOMETHING in her back and she goes limp, he then starts literally absorbing her so obviously you jump at him trying to attack but he dodges.

Doma: "Woah... That's dangerous! Don't try to cut me while I'm in the middle of absorbing someone!" he says with a sickening smile.

When you look at shinobu, she was mostly absorbed by now, only her stomach and up were free at this point, her arms were partially absorbed but not fully and you couldn't see her face since he had it against him.