Gigabird can tank for him and make him stronger. She can also convince the other heroes to reconcile with him, or at least give him the benefit of the doubt and let him prove himself through time. Just letting Naofumi leave like that is the worst decision if her goal is for the heroes to reconcile and become stronger.

What is she even doing right now? I just wished they explained how she is occupied.

The kill all the 4 heroes doesn't seem to be in her to do list anymore after he gave her a lap pillow.