
I don't think the older brother regressed or else he would have been much more emotionally stable the second life around after losing his sister because the OGFL tamed him. I think he was just worried about the New FL dying because the first time she helped ML, she was out for two days. Second awakenings are always more chaotic, especially for S-Tier espers it seems like. And his whole family thrives off of S-Tier espers and guides.

I dont think this indicates that he regressed. It was more of an obvious outcome, especially since it's an S Rank awakening which A ranks are already having a hard time guiding - much less a B rank like her. Death is the most likely outcome. Anyone could see it's too dangerous but the school had no choice but to send her and a few others.
He just didn't want her to get hurt. And besides, if he did regress, he would appear more stable than he is right now.
So the Ml's older brother and the pink haired girl for sure have lived before and are regressed ( i think that's the word) BUT LIKE at first i thought fl and the older brother were cute together asf but fl and Ml have such chemistry it's sweet, romance wise if older brother and the pink haired girl end up together ( finally) it would be perfect considering their descriptions of personality