idk if you've done this but what would an Heir of Doom be like/be capable of doing. how would doom work for them and ALSO how could they "become" doom?

The thing to have as a distinction here is that Heirs don’t ‘become’ their Aspect directly. You would have more luck saying Maids are the ones that Become their Aspect, or rather, are ‘Made out of It’, and even then the interpretation is sort of joke-y at times, but still noticeably there. Either way- This ‘Heirs become their Aspect’ comes from the fact that they are, indeed, very malleable, and as John Proves, he can even change himself into Wind- Or rather the Breeze Changes him. Sure, he can poof at will, but the very first time we see it is very much an automatic reaction to protect him- Just like the Windy Thing several times during the Session prior to his Ascension. They also ‘Become their Aspect’ in the fact they are CONSUMED by it if they cannot control it- Equius being voided out to the point his blood is used to blot out information, Mituna- Relevant as a Heir of Doom, being Consumed by the burning of his Psiioniics, while protecting from some Doom that was going to befall the Session…

As such, what would the Heir of Doom do? Change Doom, and be Changed by Doom, and Changing Through Doom. They’d be the ones to hold the power to both allow Doom to take over everything, or Change their grim fates by protecting everyone from Doom. Mituna knew shit was going to go down, and tried to warn the others, but Knowing and Guiding is not his forte- He’s knot a Seer after all. As a Heir, he was the only one who could STOP whatever calamity was going to happen, take direct action against it. And as we see, not only did he Change the sure Doom that was going to harm everyone- He Changed it through his own Doom, an act of self-sacrifice to protect those he cared about.

But I know what you want. ‘Becoming Doom’ didn’t mean you wanted the specifics of how Heirs Change, or to go into detail how technically that sacrifice of his own mind is in itself Becoming Doom. You want the cool equivalent of John poofing into wind but for a Doom Player. And I’ve argued in the past- Either lightning or fire- Specially Fire, could be associated with Doom. Technology and Psiioniics tend to be linked as well, so maybe ‘Becoming Doom’ means fading into a burst of flames a-la devil, or maybe they’d be kind of a glitchy entity that zaps into sparks of electricity or collapses into Code Itself.