Since you're already have Castoria, I'd say this is the priority :

Melusine - Serenity - Others. I don't know about Reines, but if you still want to make sure the grails are in good use, I guess don't grail Reines. Who knows if we get 2 new Artoria rather than 1.

If you want the FP to come rolling in, Reines with Bella Lisa will be everyone's favorite pick. Gives her a little more survivability and punch to her normal cards.

But actually Serenity. Reject power and meta. Return to poison memes.

I personally would have pick Serenity cuz she is waifu. I hate lolis so Melusine is not an option for me)) I am not a fan of Reines so I'll pass))

Just pick for your waifu

@Mujou1 no. do not grail those

be like me and grail your kawasumi ayako

I think he already have all of them grailed))

Thanks for all the advice guys. For now I'm holding off.

@Mokakeyk You hurt me deep inside with that :D Props tho :)

I'm still waiting for Archuria to come back (I started after her last banner two million years ago). I have 1020 SQ now and 900 of those are for her or Maid Alter (or any new version that might come out, gotta save still...).

All my Artoria except Lily are grailed to 100 (Lily is my gacha luck charm, so I literally level her up with low rarity exp and just when I roll).