The 4 Archfriends
In keeping with Rex's theming as a hero that does things like he's the dark lord, his structure of allies mirrors that of similar villains. The hierarchy, in trope speak, would be Rex as the 'Big Bad', Mel Chilikov as his "Dragon" and an "Elite 4." As a reference to Final Fantasy's recurring 4 fiends/archfiends, these 4 are OOCly called the 4 Archfriends.
Being utterly shameless, the main reason I haven't fleshed out the Archfriends is I'd love other people to create characters to fit into the roles.
Ideally, each should be suitable for a role as a recurring boss or as a member of a heroic party, quite possibly starting more fitting for the former and leaning into the latter as time goes on. This doesn't necessarily mean they have to be bad people as such- just that they tick some boxes that the bad guys usually do. Having unconventional motivations for their role is highly encouraged, as is being an alternative take on a stock character. Rex, for example, is an unusually grim and miserable chosen hero, but a weirdly kind shadowy lord who just wants to go home. Mel is a take on the girl next door left behind at the hometown trope, except rather than the typical sweet-hearted waifish girl waiting for the hero to come home she's a burly bruiser that refuses to miss out on the adventure and often acts as his bodyguard. While a four-way theme (elements, horsemen of the apocalypse, four auspicious beasts, cardinal directions, seasons, card suits, Teletubbies) would be cool, it's hardly necessary. If you want to get needlessly idiotic, a four-way theme of four-way themes in which each member has a different theme ("I am [pending] of Earth!" "I am [Pending] of War!" "I am [Pending] of Spring!" "And I am [Pending] of Clubs!") would be on-brand for how poorly everything goes for Rex. They're sure to be a bunch of weirdoes, but they should all be genuine and close friends... eventually.
Some basic ideas I've speculated on that may serve as inspiration, mostly as how they're introduced without much thought to how they'd develop-
A cleric/paladin of a religious order that is based around assisting the hero. Possibly profoundly disappointed in the one they got. Alternatively, they have a fanatical reverence for Rex which kinda creeps him out.
Similarly, a seer who has foretold they'll be the hero's companion and hates it. It's not fair. Possibly continually attempts to escape fate and accidentally fulfils it.
Someone whose primary reason for joining up is a rivalry with Rex. Particularly suitable would be the prodigal young mage that taught him conventional magic and was quickly equalled/surpassed by Rex.
An older, jaded, retired sort who, instead of the usual trope of being given hope by the hero is horrified about how badly things could go without them.
Someone who is in it for personal gain. Flat out don't care about the world, just want to get paid. If it's a thief type character, they can quite easily be Rex's cousin (his mother was a 'princess' of the global crime syndicate the Royalty of Thieves and her twin sister now rules it as queen). Could also easily be the daughter of Helen's nemesis Jijang Eun.
A person saved by Rex from some horrible fate that considers him to be their personal saviour and becomes intensely loyal/idealises him (possibly a longterm slave whose warped understanding of relationships puts Rex in the 'master' role). Rex would take advantage of their devotion but also try to live up to their expectations.
You gotta have a 'last of my kind' character in these things. Last of a species, a race of humans, a famous bloodline etc. During the enormous war that made the world post-apocalyptic, many races were nearly wiped out.
A full-blown lunatic that just loves death, destruction and mayhem and being a weapon of Rex's gives them plenty of chance for it. They need Rex to keep them from being a menace and be used constructively. Potential spin on that, bloodthirsty lunatic that needs Rex to find acceptable targets, not wanting to be a bad guy hurting innocent people.
Similarly, a mad scientist type that doesn't care how their creations are used, just that they got to build them.
A royal/noble person that wishes to use Rex's plans for strengthening humanity to further either their country's goals or make themselves the ruler of their country. A character whose explicit purpose is the recreation of the Global State with themselves at the head is a more extreme version.
Someone very helpful and pleasant with a good heart who would be perfectly in place amongst the most heroic of hero groups (personally picturing an all-loving healer type) who somehow gets stuck with these trash fires and becomes an angry chain smoker with anxiety.
A creation of Rex's, such as an android or unique type of Phantom, that obtains full free will. Maybe does so immediately and just kinda pretends to be an automaton because, hey. It's what they were made for.
An assassin/bounty hunter/cop that comes after Rex and co for their shadowy conspiracy work, but because it's actually doing good, becomes a part of the gang to make sure it stays that way.
A completely feral person who doesn't even talk that is taken in. Probably meant to be temporarily so, but gets attached to the gang/one member of the gang. Who are they, why are they here, what's up with their abilities? Who knows.
Being utterly shameless, the main reason I haven't fleshed out the Archfriends is I'd love other people to create characters to fit into the roles.
Ideally, each should be suitable for a role as a recurring boss or as a member of a heroic party, quite possibly starting more fitting for the former and leaning into the latter as time goes on. This doesn't necessarily mean they have to be bad people as such- just that they tick some boxes that the bad guys usually do. Having unconventional motivations for their role is highly encouraged, as is being an alternative take on a stock character. Rex, for example, is an unusually grim and miserable chosen hero, but a weirdly kind shadowy lord who just wants to go home. Mel is a take on the girl next door left behind at the hometown trope, except rather than the typical sweet-hearted waifish girl waiting for the hero to come home she's a burly bruiser that refuses to miss out on the adventure and often acts as his bodyguard. While a four-way theme (elements, horsemen of the apocalypse, four auspicious beasts, cardinal directions, seasons, card suits, Teletubbies) would be cool, it's hardly necessary. If you want to get needlessly idiotic, a four-way theme of four-way themes in which each member has a different theme ("I am [pending] of Earth!" "I am [Pending] of War!" "I am [Pending] of Spring!" "And I am [Pending] of Clubs!") would be on-brand for how poorly everything goes for Rex. They're sure to be a bunch of weirdoes, but they should all be genuine and close friends... eventually.
Some basic ideas I've speculated on that may serve as inspiration, mostly as how they're introduced without much thought to how they'd develop-
A cleric/paladin of a religious order that is based around assisting the hero. Possibly profoundly disappointed in the one they got. Alternatively, they have a fanatical reverence for Rex which kinda creeps him out.
Similarly, a seer who has foretold they'll be the hero's companion and hates it. It's not fair. Possibly continually attempts to escape fate and accidentally fulfils it.
Someone whose primary reason for joining up is a rivalry with Rex. Particularly suitable would be the prodigal young mage that taught him conventional magic and was quickly equalled/surpassed by Rex.
An older, jaded, retired sort who, instead of the usual trope of being given hope by the hero is horrified about how badly things could go without them.
Someone who is in it for personal gain. Flat out don't care about the world, just want to get paid. If it's a thief type character, they can quite easily be Rex's cousin (his mother was a 'princess' of the global crime syndicate the Royalty of Thieves and her twin sister now rules it as queen). Could also easily be the daughter of Helen's nemesis Jijang Eun.
A person saved by Rex from some horrible fate that considers him to be their personal saviour and becomes intensely loyal/idealises him (possibly a longterm slave whose warped understanding of relationships puts Rex in the 'master' role). Rex would take advantage of their devotion but also try to live up to their expectations.
You gotta have a 'last of my kind' character in these things. Last of a species, a race of humans, a famous bloodline etc. During the enormous war that made the world post-apocalyptic, many races were nearly wiped out.
A full-blown lunatic that just loves death, destruction and mayhem and being a weapon of Rex's gives them plenty of chance for it. They need Rex to keep them from being a menace and be used constructively. Potential spin on that, bloodthirsty lunatic that needs Rex to find acceptable targets, not wanting to be a bad guy hurting innocent people.
Similarly, a mad scientist type that doesn't care how their creations are used, just that they got to build them.
A royal/noble person that wishes to use Rex's plans for strengthening humanity to further either their country's goals or make themselves the ruler of their country. A character whose explicit purpose is the recreation of the Global State with themselves at the head is a more extreme version.
Someone very helpful and pleasant with a good heart who would be perfectly in place amongst the most heroic of hero groups (personally picturing an all-loving healer type) who somehow gets stuck with these trash fires and becomes an angry chain smoker with anxiety.
A creation of Rex's, such as an android or unique type of Phantom, that obtains full free will. Maybe does so immediately and just kinda pretends to be an automaton because, hey. It's what they were made for.
An assassin/bounty hunter/cop that comes after Rex and co for their shadowy conspiracy work, but because it's actually doing good, becomes a part of the gang to make sure it stays that way.
A completely feral person who doesn't even talk that is taken in. Probably meant to be temporarily so, but gets attached to the gang/one member of the gang. Who are they, why are they here, what's up with their abilities? Who knows.