Can be a harem but main girl must be Grayfia please
To tie Fate with the others have Lucifer or Bellatrix and the like living(like Scathach) or dead be summonable from the throne of heros.
Femharry is the protagonist instead of both Ichigo and Issei and maybe Shiro depending on which version of Fate(not Cheldea yet that comes later) you want to do they can be side characters or from different older timelines that want to help her not make the same mistakes they did. Hogwarts does the tournament when ever but I'm going to do 7th year. Jasmine(trying to keep to fan lore of Lily's family naming tradition) gets adopted by Arthor/Atoria(Papa/Mama) and Morgana(Mom/Mother) with sibling Mordred(Bro/Sis) who were revived and made immortal by the Pendragon family from DxD cause they were attacked an nearly went extinct after 2nd year maybe she ran away after a week at the Dursleys finally fed up with everything and ran into Mordred who was exploring. Mordred who is a squib/low magic circuits could feel the magic on this thought to be 9/10 year old instead of the 12 year old girl she is decides to get to know her and Jasmine a good judge of intent when not emotional/positive attention starved and cause her magic is not warning her against Mordred lets them. After learning about Jasmine through a lot of coaxing decides that they will take her in no matter what their parents think (Mordred went she is mine now in a platonic way) cue confused parents but happy Mordred is taking responsibility and action for something in a non violent way little did they know though they would and will agree when they find out what happened to Jasmine. After they found out and went to Gringotts to adopt and check her inheritance which is needed befor they can adopt her it just makes them madder cause Dumbledore and maybe selective Weasely's and Granger. They find out about her dormant Shinigami and Hollow blood from James side(could tie into the Peverell line) and Quincy and maybe devil(Lucifer) or some other hero(Gilgamesh just for Atoria's reaction 😂) blood from the throne of heros on Lily's side, please note that if Voldemort uses Jasmine's blood to resurrect he does not gain any powers. After reading the inheritance test and blood adopting Jasmine they decide as a family to travel the world and make connections for later like Cheldea later cause the Pendragon family(Rulers) will be living summons like Scathach . To tie the other three together maybe have the holy grail war first while its happening Jasmine(15/16) as a master meets(Morgana taught her magic craft and HP spells) Grayfia who is monitoring it for the devil's Gabriel for the angels and big bro Azazel for Grigory and Kisuke and Yoroichi for the Shinigami(later all the above become teachers for respective fields and for the females maybe harem members/peerage members Grayfia obviously is the queen) by accident and be mistaken for a hero spirit cause of her restrained power, she is wearing gloves to hide her command seals and she's with Shiro(low ranked magus or older version), Rin or Sakura(savior complex never went away or saw her home life for what it is) someone she has an alliance with and is family approved of, even though she summond original timeline saber/Atoria and not her Papa/Mama (this would be hilarious) you can decide how this goes. Timeskip a year and Jasmine and co(16/17) is in Karakura/Kuoh same town diffrent districts(there a non aggression agreement kinda like a you do your job ill do mine with the Shinigami) but 1(2) giant school(s) in the middle(before co-ed) and is a second year (Issei's class Ichigo and co are also there) Jasmine's dorment devil blood if going that route starts to act up after a month of school because of Rias and Sona the 2 feel it and go to investigate find and befriend Jas and help her get caught up with the devil politics and ext. Before everything hits the fan Jas can befriend everyone including Issei who she sees as a troublesome little brother maybe and everyone(the whole school) learns that she is protective and supportive of those she cares for like helping Ichigo with the ghost, Orohime with perverts and bullies and reigning in Issei when he becomes to much Jas is the definition of mom friend. Issei could get attacked first because of the twice critical (not boosted gear that goes to Jas or maybe Mordred after their resurrection) then every thing kinda spirals from there. When or if the tri wizard tournament happens Jas when summoned as a Satan class /equivalent for bleach has her peerage and thier's if they wanted one(cause there at least all high to ultimate class (DxD) (this is when the wizarding world new they f'ed up)😰