Treating the MC as a protag of a time-travel story makes him more likeable to me. He's trying not to screw up the timeline he wants to occur too badly, at least as it pertains to people he likes. His sister being there and deliberately trying to make massive changes throws things out the window...
Mega-skeleton-cow should be useful for heavy lifting and moving stuff at the very least. Pretty intimidating guard as well if you aren't familiar with it.
Be kind of funny if the MC agrees that she's a bad person and dips out on her. Yeah she's aware she was a bad friend but taken against her actions since he's known her there isn't much if any evidence she's changed. Hard to trust someone like that, particularly with your life.
@Tamerlane As long as the "what" his heart is pure of isn't defined he should be fine. His heart is pure angst.
Unrelated but why does Keyaruga have Saitama facial expressions every now and then? Last page this chapter was one of them.