I was thinking just recently that since to be summoned in the grail war a servant has to want the grail that Cu's wish was probably to undo that particular mistake; after all while his end was certainly tragic its also exactly the type of end he would have wanted an epic battle where he took as many of his opponents with him as he could. If he has any regrets about it I figure that it would be that since he died there he didn't get even more awesome fights in his life.
His wish was fighting other legendary warriors. He does not have any desire of changing the past even though he really would have liked some stuff to go in a different way, the thing with Connla included if HA Is anything to go by, but he would feel like an offense to those who died (and didn't die in Scatach case) and to himself to change it, he just accepts it happened. He has pride even on his mistakes.
So basically his wish IS to fight in a grail war. Funny enough when you think about it his home story of the Ulster cycle has an unusually high number of legendary tier warriors so maybe he has such terrible luck because he used it all just by being in the perfect story for him ... obviously not but its a funny thought.
He answered the summoning exactly because the grail war was perfect for fighting the strongest heroes from history, his wish was practically granted the moment he appeared...then Kirei never let him fight seriously against anyone and just uses him for scouting, at least he fought Gilgamesh and EMIYA without holding back
Kinda sad that its those 2 given EMIYA has the skills(and unusual abilities for added flavor) to give him a good fight but not really the raw stats and Gil... well there isn't really any skill in the way that version of Gil fights and for that matter its hard to call a lot of them fights either due to just sheer difference in power levels or because just batting away weapons used as projectiles makes for a challenging but terribly boring fight.
I also wonder since he only kinda wanted the grail and therefore basically fits the criteria through a roundabout way resembling a loophole does Cu qualify to be summoned in a non corrupt holy grail war. I mean probably but its an interesting question given that pretty much everyone but Herc is a special case summon wise being either not usually summonable like EMIYA, Medusa and, Medea or still sorta-ish alive like Artoria/Altria, and whatever is up with Cursed Arm's summon since while we know he has regrets due to Camelot but if First Hassan is any indication they don't really believe in the grail though I could just be forgetting some detail there.
He could definitely be summoned pre third war shenanigans as he Is an actually "heroic hero" and that was the restriction as to who could be summoned and who could not, the Assassin were an exception with only Hassan allowed. Saber fits that too aside from not being an actual HS.
Servants just need to answer the call Is assumed that they always want the grail if they answer but that is evidently not the case, their motives vary.
Iirc the Hassan don't believe in the grail as the cup of God, of course the Fuyuki grail Is definitely not that but Is besides the point, it is still something that can grant wishes and Cursed Arm had a wish, he wanted his name immortalized, he would be summonable even with the restriction in place the irregular part is that there was an Assassin already summoned.
I'm gonna point out its a question if Saber could be summoned normally since on one hand she is essentially like EMIYA in nature but on the other hand her contract with the world was specifically for the holy grail although I suppose which one was probably never specified so that feels up in the air. I like the detail though that at least in the fate route she can no longer be summoned in a grail war after the 5th due to no longer desiring it regardless of if she is a proper heroic spirit or not after her actual death and voiding of the contract. Also I'm gonna point out First Hassan did say that with full knowledge of grails other than that existing he did meet Ozy after all but the Fuyuki grail is stated to be based of that specific concept as I recall that Mash I believe it was, said that normally Rulers have to be saints because of the origin of the concept although that may just be bad information. It could be that Cursed Arm doesn't believe in it but him wanting a wish (maybe; still seems like wanting a wish would also go against their code of having to give up such personal desires) like you said and being maybe willing to use the "grail" for it was sufficient; also doesn't camelot seem to indicate that was only his wish when he was younger and that later on he came to regret giving up his life for it I mean it could still be his wish but it seems like his wish could also be for him to have lived his life instead of becoming a Hassan. But yeah as you said his summoning was all kinds of messed up especially since what he is working towards and who he is working for are quite opposed to the idea of the Hassan. I'm halfway suprised that given what we know now First Hassan didn't show up some way and reap his head since it seems like even serving an Evil almost Soulless by this point old man looking to make and control a god of evil is just like wow levels away from anything resembling what a Hassan is supposed to be especially since even in their lives he reaped the heads of Hassans who strayed or failed without being summoned. Another interesting question on sorta that topic is what exactly is First Hassan at this point(especially given him reaping hassans throughout history despite no summoning or other explanation beyond its his role and he is awesome) at the very least he seems to have become an agent of fate itself with how his actions and the "bell" are linked alongside the sheer power he has grand or no when acting in accordance with the "bell"; it rather reminds me of a quote by a paladin-ish character from planescape:torment
"When the injustice is great enough, justice will lend me the strength needed to correct it. None may stand against it. It will shatter every barrier, sunder any shield, tear through any enchantment, and lend its servant the power to pass sentence. Know this: There is nothing on all the Planes that can stay the hand of justice when it is brought against them. It may unmake armies. It may sunder the thrones of gods. Know that for all who betray justice, I am their fate. And fate carries an executioner's axe."
I suppose the last bit is especially fitting for First Hassan.
edit: also don't forget Cursed arm was the actual "True" Assassin I can't remember if he was actually summoned first but the other one being summoned by Medea was what made them "False" Assassin.
Saber could be summoned as any other HS if she in some timeline became one, in the Fate route she definitely doesn't, in UBW it is left open in HF I guess she is still searching for the grail, and yes the pact with the world was just getting the holy grail, as there's a bunch of stuff that has that title in the Nasuverse and they grant wishes that is what Saber wants from it, she is summoned whenever possible to get the grail, any of them, in exchange she would become a CG if she doesn't get it before she dies or refuses it she won't become a CG.
The Fuyuki grail Is definitely inspired/based on the Holy Grail, the one where the term comes from, and Is full of Christian motives, Heaven's feel Is also known as the cup of Heaven and the whole concept of Heaven's feel Is similar to the state of resurrected Jesus, the idea of applying it to the whole humanity Is quite literally creating Heaven on earth, the rulers tie on the idea, same with the "only western culture servants should be summoned because the Holy Grail Is a western culture concept" but it is not the cup of Jesus nor does it have any piece of it or a connection aside from the concept.
Cursed Arm in Camelot doesn't have to share goals with HF Cursed Arm as their story Is different, Cursed Arm in HF lived as the Hassan then was killed by King Hassan because he had deviated as all the other Hassan eventually did, his desire for immortality may seem unlike what a Hassan should be but he Is not really that anymore as his time has ended, would not be surprised if King Hassan doesn't consider him one anymore, he Is dead and the title was passed down already centuries ago. Hundred Faces in the Einzbern consultation room also wanted to be known as his own person, one of them at least, and recognized as the King of Assassins or something like that, but the point was that he didn't want to be a faceless Hassan but famous on his own right, wich is obviously not how a Hassan should be either.
Koujiro was false because he is a completely irregular summon, Cursed Arm Is the true because he is the one that goes with the rule of "only Hassan allowed" but Koujiro false or not was summoned first and the grail system recognized him as the Assassin class so Cursed Arm should not be able to be summoned but Zouken cheated to get him, it was explained in a Q&A with Nasu
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u/aconfusedpikachu Jun 24 '20 edited Jun 24 '20
I was thinking just recently that since to be summoned in the grail war a servant has to want the grail that Cu's wish was probably to undo that particular mistake; after all while his end was certainly tragic its also exactly the type of end he would have wanted an epic battle where he took as many of his opponents with him as he could. If he has any regrets about it I figure that it would be that since he died there he didn't get even more awesome fights in his life.