Lion is less concerned with his returned brothers than he is with the emperor and gman. Lion’s whole deal is loyalty, particularly to those above you (we’re still working on being loyal to those who rely on you but we’re getting there). To him, emps accepting magnus back into the palace isnt so different from him collecting the Risen, but emps’ refusal to take the reigns from guilliman despite his brother’s measured response to stuff like the ecclesiarchy is baffling to him. He’s mellowed out a Lot since imperium secundus, but his most basic thought process does not understand why they aren’t all just wiping planetary governments and starting from scratch now that dad’s back. Why go through the trouble of installing the triarchy when you leave all the rest of the stupid 40k imperial bureaucracy anyway? Why is dad allowing gman’s 20 stupid space books of space rules when the first one sucked anyway?? Why isn’t dad in charge???

I say most basic thought because, again, he’s had some time, he’s done some Introspection, he has admitted to himself banishing people for mistakes is not always the neat and tidy solution it’s made out to be in his head, and that his paranoia is a problem, it’s just hard for him to change that pattern of thinking. also he’s not entirely wrong i mean. gman is slow going because he’s got approximately the entire universe on his plate but like. some of this stuff feels like something that should have a ten-step removal plan. right??? point is it’s complicated, and he doesn’t have a clean solution and is actively restraining himself from enacting his own version of a ‘clean solution’ which he’s at least learned is maybe a bad idea without running it by dad first.

In the meantime dad said to continue gathering the Risen, so that’s fine he can put his energy into that. Dad also did not say shit about the risen being not codex compliant so take that gman. so lion currently is largely occupied with trying to get his legion in order, which is a bit like herding cats pun absolutely intended. lion is constantly fighting new fissures between what he and the risen envision and what the newer astartes of his geneline are used to expecting, issues that run hot enough that there are some days where it feels like they’re creating fallen instead of saving them. it’s a constant uphill battle even with the newfound self awareness. running back and forth to gather bits of his old legion means he’s mostly out of the way of his brothers, and that’s just fine as far as he’s concerned.

That said, him and his arc are more central to Updated Codex than one might expect. For one, lion is the one who tattles on gman to emps. He takes one look at juno and goes

'i'm telling dad!!' and runs off to do just that, forcing gman to introduce juno to the wider imperium. she’s about 4 at the time.

An older Juno, as stated in the snippet below, has been boots-on-the-ground for fallen retrieval missions; in fact they were probably some of her first joint campaigns outside of ultramar/ultra successors. Lion has seen her work as and with astartes, and generally is alright treating her the way he does his formerly wayward sons.

that doesn’t mean he trusts her. The paranoia didn’t magically disappear. when she gets her own little specialist squad consisting of some weird serf, the child of a traitor, and a xeno spawn, He manages to get a dark angel attached to their retinue, and instructs him to report on their actions regularly.

Juno isn’t impressed.

Melwas is a brand new Dark Angel looking to prove himself in a time when living legends, tarnished though they may be, walk amongst them and his primarch is personally watching every move he makes. Mel has a massive guilt complex, for both genuinely enjoying the oddball squad’s company (a betrayal of his mission) and for spying on them (a betrayal of his friends). It’s a lot of pressure, which isn’t helped when, upon reuniting with a former neophyte friend of his, he is promptly subjected to a barriss offee style turncoat plot where his friend tries to kill him (and the squad) in an effort to make a point about how the DAs are losing their way of life, yadda yadda, angst, yadda yadda etc. yaaaaay!!!

He gets a weird dog and some hugs from his friends and maybe his dad figures out how to tell him in words he was handpicked for the oddball squad because lion is actually quite impressed with his level head. maybe lion will go the extra mile and figure things out with luthor and mel can make out i mean up with that friend who tried to kill him or something. who knows.