The timing of events is a little off, but what about Brain being the killer?
Definitely also still on the table.
Like said, the only ones that can be definitely ruled out are Skuld and Ephemer because we know where they were at the given time.
So the Killer would have to be one of the new Leaders right?
If Strezilia is Lauriam's sister I feel like we could cross Lauriam off the list but its still possible he could've killed his own sister as dark that may seem.
Brain is pretty sketchy and it wouldn't surprise me if he was the killer.
Now it would surprise me if Ephemera, Skuld or Ven is the killer. They all seem pretty pure to me but we know that Ventus at least has darkness within him, when Xehanort made Vanitas out of Ven's Darkness, there was more Darkness than light.
Ephemera had an interest in the Book of Prophicies when talking to Ava but now it wouldn't make sense for him or Skuld to replace Strezilia because I'm pretty sure Ava made them leaders, I know she at least made Ephemera a leader but I don't recall if Skuld was made a leader. Could they have still killed Strezilia after being made leader? Maybe.
Not absolutely.
The new leaders didn't know before the first meeting at the Keyblade Graveyard who the other four leaders would be, yet Strelitzia's assailant had to know she is one if the goal was really to just replace her instead of i.e. just preventing her from telling the Player Avatar something they aren't supposed to know.
I didn't spend much thought on it up to now, but re-watching the cutscenes in Strelitzia's house her Chirithy seems to be very worried for some reason about her intention to warn the Player Avatar and/or recruiting them to the Dandelions.
Chirithy: "But Master Ava told you not to say a word to anyone."
Strelitzia: "I'm gonna recruit him to the Dandelions. I won't say a word about anything else. Good night!"
Chirithy: "I'm not sure I like this!!"
It's also a little weird that her own Chirithy seems to have second thoughts about her qualification as a leader, voicing them right after directing her towards where
the Chirithy thinks he saw the Player Avatar:
The next morning, Strelitzia is waiting for Player, when suddenly Chirithy says he saw him/her. They go to where Chirithy saw the Player.
Chirithy: "She… a Union Leader… really?"
Then there is the actual assault and Chirithy claiming it is all his fault?
Why? Because he doubted her? Because he lead her to this location in the first place?
They enter a house, but nobody is inside.
Chirithy: "Maybe my eyes were playing tricks on me."
Strelitzia: "Helloo! Is anyone here?"
Chirithy: "I guess I was wrong."
Strelitzia: "Well, it was worth a shot. I'll head back to the Fountain Square.
Chirithy: "Okay. I'll keep searching."
Chirithy: "Hm?"
Strelitzia: "What?"
We hear a Keyblade strike someone. (this was cut out in the GLOBAL version for some reason!!) Strelitzia and Chirithy are on the ground, her book next to her. The attacker takes her book and wanders off.
Chirithy: "Why...? Strelitzia…"
Strelitzia slowly gets up and hugs her Chirithy.
Chirithy: "I'm sorry. This is all my fault..."
Maybe I'm seeing things but maybe Strelitzia specifically trying to aid Player is another reason or the actual reason why she had to disappear.
---
Everyone has darkness within them, that's not really a definite criteria.
When Xehanort made Vanitas that is not only after whatever disaster happens that leads to Ventus landed in his hands in the first place which could further fuel Ven's Darkness, it is also not true that there was more Darkness than Light in terms of quantity. The part of Ventus' heart that is missing symbolized by his cracked Awakening station is roughly a quarter and about that part Xehanort writes in his reports that Vanitas took more of Ven's heart than he was supposed to thus further weakening Ventus who was already in peril due to having been nearly mauled by a bunch of Neoshadows.
It is a given however that Ven's darkness was rather
deep due to already experienced trauma which most likely stems from both his experiences in the X-era including having to witness the war and deal with possible survivor's guilt as well as whatever "training" Xehanort put him through beforehand.
This all isn't really an indicator for a capacity of intentional murder though as Ventus seems to dislike fighting and only resort to violence if he must as seen in this newest update when he objects to the PvP-feature.
Ephemer and Skuld can be ruled out at least as those actually doing the strike that does Strelitzia in as we know they were at different locations when it happened.
Ephemer was already in the Unchained realm to set things up and Skuld was with the Player.
It doesn't rule out one of them "ordering" the deed yet just like Ven, their personalities and outlook do not really fit such a drastic measure.
Blaine is definitely still suspicious and out of the new Union leaders he is practically the one we know the least about after Lauriam.
At this point I think Lauriam is the red herring and Brain is the shady one who might've at least set up the murder.
He's sketchy AF and the fact that his face is always partially hidden does not bode well.
Also he's not even trying not to be suspicious and ruthless anymore.
Possible, but I won't decisively rule out Lauriam yet nor settle on Blaine as the definite culprit.
Is he really
ruthless or has he just a more pragmatic stance compared to i.e. Ven and Skuld?
I agree though that his behavior comes over as somewhat shady if not even partially manipulative as he seems to not only be the one to most quickly agree to implement things right away he also plays this whole "Ephemer is
the leader"-mantra up a tad too often for my taste.
It comes over sometimes as if he's subtly trying to put Ephemer under more stress and divert at least partly responsibility for decisions made.