Warning: Spoilers Off applies to Tearjerker pages.
Rikka throughout the movie has shown she is not at all happy with Yuta choosing to become Gridman again without a second thought, with Utsumi noting she's worried that he may get hurt again (Like when he got stabbed in Episode 11 of SSSS.GRIDMAN) or lose his memories again. Combined with the fact that this is the real Yuta, whose Chronic Hero Syndrome is pushed into overdrive this second time around, it leaves the poor girl wracked with worry that he's putting himself on the line again.
Earlier when Yuta describes Rikka and Utsumi's stage play as their, Akane's, and Gridman's story, Gridman asks about Yuta's story to which he replies that he doesn't remember any of it, so his own story isn't really there. This undoubtedly twisted the knife even further for Gridman, who's already feeling terrible for his actions, but having to hear from Yuta the results of it more or less makes it worse for the poor guy.