Well I've been thinking further about this
Story is 'light based magic kills some people in demacia, garen is tasked with finding the person, vayne is the bigger player in this though because of her expertise, she tags along"
in general this would lead to people assuming that lux is the perp, but there is at least one other light based damage champion in the game who could be present.
Often fights the undead, but he isn't limited, he generally dislikes various evil magic doers, and in many ways has a more sane and balanced variant of 
's role, But why would he be in Demacia? He's generally dealing with the shadow Isles.
Well theres the order of the black rose, which features such characters as 
and 
but more relevant to lucian's interest would be 
and especially 
Lucian is drawn to track down elise from what he finds on the shadow isles: the corpses of her victims. He first goes to Noxus but finds her absent, instead he is forced to face off against and , Possibly coaxing information out of one of their henchmen on elise's whereabouts
Well after his fight, he travels to demacia where the spider prophet is reported to be, the rose's chief member who also happens to be the CiC of Noxus dispatches one of his best assassins 
with a team of noxian infiltrators
So that sets the stage right there
Lucian did it, he killed a bunch of noxians with his light casters while seeking his quarry: a shadow island/noxian character, This would provide a good contrast to a focus on vayne's half of the story, while it would also allow for some development for the 
subplot
being in noxus would be a big deal, and if swain knew then it would be a larger setup, likely a plot against the crown all together
could also be alongside katarina for this one, possibly with a grander target 
) which would give potential for to change sides and overcome a man who is considered her better at her job (Noxus's best assassin)
So Lucian kills some noxian assassins with light based bullets, it leads you to think it was actually lux, garen and vayne start pursuing lux because of the rumors about her. Vayne and Lucian have some sort of Paradoxical interaction, are they allies? are they enemies? They share many of the same targets but can they actually beat eachother? A stalemate where each would kill eachother at a moment's notice, but they allow eachother to live because of their targets
lux would have a lesser role, Instead focusing on and on Both dichotomies would actually have a good balance, with one character feeling fleshed out enough to give some room for the other to grow more naturally, as both and could use some development
This also sets the stage for a pretty comfortable Demacia vs Noxus story type, where the actual end of the journey is less interesting then the journey itself, It could also result in garen getting a dues ex machina in not having to kill his sister, but her being outed to him. He could defend her and disown her at the same time, showing that through his thick honor he loves his little sister more.
