I am dead, after writing a long reply my browser fucking refreshed because it didn't count this as beast lair so it sign me out automatically since the settings aren't considered the same so my profile was checked off as remember me & stay logged in. *INTERNAL SCREAMS* Well going to have to rewrite everything...
Edit1:Trying to remember everything off the top pf my head is hard
Editt2: Damn can't shake the feeling it was better written the first time
Edittt3:Well it is what it is, can't remember exactly what is missing, but this is about the gist of it
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This is exactly something I thought someone would say, though I do think I did better than just a recolour XD.
As for during his time at Chaldea I don't think it is too far off from other mages we have been introduced to & as for after it plays into the fact that he is a counterpart to Fou & also a Beast of Comparison. "...ability of "Comparison" lets him feed off the competition and growth of Humans and their negative feelings toward it, allowing him to become stronger than his opponents." & also in the original development the toxic behaviour of players was supposed to empower the BEASTs ("The game originally was planned to be a PvP game on the PC (back when it was being shopped around as Fate/Apocrypha), where gamers' Jerkass behavior would directly create the Evils of Humanity they were tasked with destroying. Nasu decided in the end that he wanted to write a more optimistic and brighter game on the smartphone."), so the more people bitch about how "unfair "OP" & "impossible" it is, the stronger they get as BEASTs of Comparison. In addition to this, replicating traits & weapons(If only I also had...), comparing PHH with the LBS, & themselves with Chaldea & Ritsuka, and such also fit well with Comparison.
He goes into the Lostbelt an angry, discontent, distant, sour, angsty youth & comes out a mature emotionally stable adult after 1500ish years isn't really a stretch. Also even after all those years he still holds some resentment towards Chaldea that he reveals when everyone from OG Chaldea(Romani DaVinci Team A Mash Ritsuka & staff) is gathered for the 1st time in the story. This is not because they didn't heal & bring Team A back, but because they didn't even try. Even with all the resources they were amassing, all the expert Servants, AFTER the Incineration was resolved & even when Goredolf recklessly tried to take them out of cryo, endangering their lives, Chaldea never really tried to help them, not even then resorting to force to stop Goredolf potentially killing them. They never drew up a ritual, treatment options, assigned Servants or tried to use Holy Grails, nothing. He is mad because he feels that even with fewer resources, time, etc... they dealt with far more difficult situations, so the only thing they must have been lacking is desire/motivation. So what he is truly hurt by isn't the fact that they didn't succeed but the fact that they didn't even try anything. As the one anchoring Team A, Peter was conscious, moment to moment, day after day, waiting for outside help, despite barely being able to perceive the outside, caught between the decision to help his teammates or let them go & attempt to recover only him & Yu if he ever felt Chaldea needed backup & yet the Alien God was the one who helped them first. He feels he was willing to do more to help Chaldea in that time than Chaldea did for them, despite their positions for who needed help & who could offer it. He is even more upset with Romani & DaVinci since they knew each other & got along well, having lived & worked together, caring about each other or so he thought. He even sarcastically asks Da Vinci to justify what she "an omnipotent genius/Uomo Universale whose wisdom & knowledge surpasses all others" lacked all those YEARS in order to try & bring them back. They were just forgotten, never even mentioned them or shared memories about them with Ritsuka.
This is kind of meta, since after the prologue they are never mentioned again until the next prologue(LB).
One of his main traits is "wrath" as I kind of wanted that to come through from what he said in Russia, his bio & the quotes section. He is disappointed by Chaldeas decisions in dealing with the Association & abdicating the duty of protecting humanity, not being careful enough with something so important & trying to leave first chance they got. He is also completely fed up & over listening to how "good" PHH, whether in the present or past the divergence points. He can't understand how anyone could honestly say that it is "better" or more "worthy" than Alvalion given how Humanity is headed for its own extinction one way or another(climate change, pollution, overpopulation, resource exhaustion, the one point where I will give Qin Huang credit), the cesspool that is the sociopathic Mage'sAssociation/Church underground world, the rampant breaches of Sapient Rights all over the world, the proportion of well off countries & people vs those who aren't, and on and on it goes, the list is enourmous. "When you say PHH is "safe & good" you must be referring to 1st world countries in the present like Japan right? Even those are also full of problems. Then tell me even putting aside how disgusting society was in the past between the divergence point & the present. Nowadays, in how many countries would you not choose to be born if given the choice? In how many countries are the people outright oppressed? How many wars or armed conflicts are ongoing that you don't even bother to think about? How many countries are there that you wouldn't feel safe going to without precautions? How many countries are there where Mash could go around without worrying for her safety, as a young lady? Any answer over 0, is still 1 more than I am willing to tolerate."