There's something interesting I noticed while chatting with a friend that I haven't really seen any discussion about on here. There's a handful of quotes in Ashes that all but confirm this new version of Takeo's bonded with some sort of entity/spirit/demon/whatever.
The Entity in the EE's mid-quest cutscene reveals why the Warden is targeting Requiem and nu-Primis (forgive the nomenclature) with the following quote:
ENTITY: Each of you have encountered… been touched by a great power – something has left its mark on your beings. The Warden of this place sensed it – sought you out – tore you from your dimensions, and drained you to take that essence for himself.
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Each of the characters has bonded with the Dark Aether in some way through an entity or artifact. For Requiem, we know it was the Sentinel Artifact found all the way back in The Tomb that teleported them here (as confirmed by Carver immediately pointing that out after the Entity's quote).
CARVER: The Sentinel Artifact… damn you, Richtofen.
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Dempsey, on the other hand, (which we know thanks to his secret dogtags sidequest) became bonded to a demon at an ancient temple by his timeline's version of Weaver and Strauss.
VEYTHARION: There it is… you were the vessel for a ravenous evil, summoned and bound into your being. Its shadow yet hangs heavy on your soul. Interesting. Your exposure to the unnatural, and being ridden by a demon undid you, Dempsey.
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As far as I'm aware there isn't really any info on what happened to Richtofen or Nikolai to be "touched" by the Dark Aether, but Takeo has more than a few quotes implying that he's been in contact with some sort of a female entity. I'll list a few of them below:
1: In my land, there are yokai who consume your ki – but they are usually female…
2: [whispering noises] Now is not the time – if I wish to know your opinion, I will ask.
3: I will not fail! She must be sated!
4: Always beware of strange voices beckoning. I speak from experience.
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So, clearly, Dempsey isn't the only one amongst the original four who've bonded with an entity. As for who this entity is… its a mystery for now, one that'll probably be followed up on in future DLC (volcano temple map, anyone?). But I think a likely candidate could be Saraxis, the Shadow, one of the many demons we met in Vanguard.
Per her own words, whenever she interacted with humans, she spent a good chunk of it doing so in Feudal Japan. So much so that the Japanese likened her to the mythical kitsunetsuki, a trickster spirit that could bond with humans.
SARAXIS: “Kitsune.” Do you know that word? I picked it up a few centuries back, when I spent time in Japan. It means “fox,” but it also referred to a sort of trickster spirit. They were said to bond with humans — inhabit them, possess them. This was called kitsunetsuki. Such a lovely language. It meant the “fox” was within you, controlling you, affecting your mind. So guess what more than a few humans used to call me? Some even offered themselves for my… kitsunetsuki. I salute the Japanese for their fearlessness. Because that’s what you have to be to bond with me. Fearless. Soldiers, servants, holy men, lords and ladies. I hooked up with anyone who was willing to take me for a ride. And what a time we had! The party lasted from the Heian period well into the Edo period, but it all came to an unpleasant end when… well… the less said about that, the better.
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Although her time in Japan was within the "pure" timeline created at the end of Tag der Toten (the one VG, CW and BO6 take place in) and not Takeo's timeline, we don't really know what happened to her or the other demons after the end of The Archon. It's commonly assumed she and the others were devoured by the Forsaken before CW, but it's possible she was one of the many "Old Ones" that would supposedly be freed after the Forsaken's defeat.
SPARAGMOS: The Devoured shall be reborn. Their scattered ashes shall be reformed. The Forsaken’s torment will be undone, when the Old Ones reign once more.
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With the Forsaken's death during the Gorgofex quest during Reckoning, it's possible she and the other demons were freed and able to once again leech their way into other worlds… this time into new and untapped alternate timelines that seem to have propped up after BO6's ending. And who better to influence than a culture she's already familiar with? If this ends up being the case, we could see Saraxis and other elements from Vanguard Zombies take a much larger role in the future.
But of course that's just me speculating. Let me know what you guys think, and if you have any other candidates for who Takeo could've bonded with.