A bit of speculation/prediction

Just some random ideas that popped into my head after rewatching the first episode. Still have no idea where the plot is going to go but I have some speculation about Agata's past and the reason for his resistance to pain.

So for the first scene in the first episode with Agata as a child, I think that maybe him and the girl (might be Sonozaki, they look similar) as well as a bunch of other children possibly, are all already part of a Kizuna System experiment. This is why when the girl falls off the building to her "death", Agata absorbs so much physical pain that it takes many years off his life, hence why his hair unnaturally turns white, possibly meaning he might not actually have that much longer to live. Agata tells them that he doesn't want to be left alone, implying either it's just the two of them in the experiment, or the rest of the test subjects have already died for various reasons.

Him already being a kiznaiver from his childhood explains why he doesn't feel pain when he gets beat up, if he was connected with a lot of other kids they would all share it. Also corresponds to when Tenga is testing if Agata's body feels pain and Sonozaki tells him "There are limits to things, you know". Not sure where Agata's amnesia came about, but would seem pretty convenient for why he can't remember already being a kiznaiver.

As for Sonozaki herself, if she was the girl who jumped off the building at the beginning, them already being part of a Kizuna system would explain why she is still alive, since they shared the pain with Agata letting her survive the fall. This is also hinted at when Sonozaki pushes Agata down the stairs and says how he survived the fall because the rest of the group shared his pain. Her being one of the original test subjects might also explain her current involvement with the second experiment. But it's also possible I'm reading too far into that and the two girls are different people altogether.

Still a lot of holes in some of these theories but just wanted to get that off my chest in case any of these are vaguely correct in the future plot, we'll see. Let me know if any of you have any other theories, really interested in where this anime is going.