Naruto Uzumaki: Legacy of the Doom Slayer
Crossover: Naruto and Doom (2016)
At a glance: the Doom Slayer gets stranded in the Naruto-verse after a teleporter mishap and eventually becomes the forefather of the Uzumaki clan (explaining their penchant for demonic chakra, their longevity, their enthusiastic combat style, and their red hair). The art of demonic runes eventually becomes the art of fuuinjitsu: an Uzumaki specialty. After many decades and over a hundred children, grandchildren and great-grandchildren (Uzumaki are frisky, who knew?) someone manages to use this art to re-open a portal to hell. Slayer leads the charge along with any adult volunteers. One Doom slayer is terrifying, but ultimately an annoyance. Dozens? Hell falls in months and Demonkind has new masters. As part the surrender agreement, the Demon Summoning Contract is penned. One of the big clauses is that the contractor and his family are "cursed" to send their eternal soul to Hell upon death (where the Uzumaki reign as kings).
Outline: The prologue chapter will be in three parts. The first part would begin with Slayer's arrival in the Shinobi Nations and subsequent meeting with a daughter of Asura Ōtsutsuki (the daughter would be an OC, no children are listed by name on the wiki). There would be a heart wrenching scene where Slayer realizes he has forgotten his own name, he has been fighting for so long. OC names him Akage: "Red Hair", he responds that its as good a name as any. The second part would begin after a considerable time-skip: decades. Shortly after OC's funeral (she wouldn't have had Slayer's longevity, but all their children do) Slayer starts looking into ways of finding her soul. He is distraught that she seems to have ended up in Hell and endeavors to find a way there to rescue her. Using some of the Argent energy embedded in his soul to open the portal, Slayer is joined by all his children and a number of his grown grandchildren on this hunt. The final and largest part of the prologue would be from the viewpoint of a demon as he recounts his memories of the first, second, and final comings of the Doom Slayer (original Doom games, Doom 2016, and the Uzumaki respectively). How he was the first to surrender to the red-haired warriors, to be chosen as their herald to the others. How life has improved in Hell for many demons after the Uzumaki took over. The rise, and subsequent fall of his master's real-world home in Uzushiogakure. This will largely serve as a exposition dump showing the audience "behind the curtain" for certain canonical events. His thoughts are interrupted by the near-forgotten sensation of a summoning being performed. "How odd, there are only a few living Uzumaki, and none have signed the contract. They must be using the Old Ways. Poorly, it seems. I'll need to help from this end for it to work. Be glad, mortals, for you caught me while I am feeling indulgent."
The first real chapter begins with a 6-year-old Naruto getting chased by a mob. He is caught and beaten, as usual, but this time his tormentors decide to get creative. One of them had found an ancient text with descriptions of some arcane rituals. What better way to get rid of a demon than to send him back to Hell? Roughly halfway through the ritual, a Hellknight appears on the pentagram and asks why they have summoned him. In the subsequent ravings to take the hellspawn child back from whence it came, someone drops the phrase "Uzumaki brat" and the demon hears it. Agreeing to take the child, he asks for a sacrifice in return for the boon. They thought the child was the sacrifice, but the demon responds that *they* are and tears them limb from limb. Carefully lifting the unconscious boy, the demon says "Come child. If you are who I think you are, Lady Kushina will want to see you again."
Naruto spends the next year or two in hell being nursed back to health and meeting his family. He visits frequently thereafter to train and socialize with his clan. Naruto will eventually be trained in his mother's nodachi and taijitsu styles, the clan's fuuinjitsu seals/demonic runes, and he gains the demon summoning contract. Naruto will eventually attract a small harem of "bad girls" consisting of at least femHaku, Kin Tsuchi, Karen Uzumaki, and Tayuya Uzumaki (Tayuya's last name is not given in canon, nor is it implied what clan she is in, but her hair color is familiar. In this story she is both an Uzumaki and Karen's sister. Orochimaru recruited both for Otogakure at the same time). Plot after academy graduation downplays the various canon fights and emphasizes Naruto's efforts to restore the Uzumaki clan including invoking the CRA and assorted bits of political skullduggery he has to go through. The overarching nemesis of the story is Root and the civilian counsel and the "final boss" is Danzo himself.