Grade 0: 17
1 Advance Party Seeker, File
2 Seeker, Platina Rider
3 Certain Kill Seeker, Modron
3 Messagal Seeker
4 Seeker, Harold Breath Dragon
4 Seeker, Loving Healer
Grade 1: 14
2 Glynngal Seeker
4 Guardian Law Seeker, Shiron
4 Rouse Seeker, Aremil
4 Lake Maiden, Lien
Grade 2: 12
4 Blaster Blade Seeker
3 Combined Strength Seeker, Locrinus
3 Crossbow Seeker, Gildas
1 Full Bloom Seeker, Cerdic
1 Blaster Blade
Grade 3: 7
4 Light Origin Seeker, Alfred XIV
3 Splitting Seeker, Brutus
Song subject to change. This build is complete five minute theory based on hype, so take this whole thing with a grain of salt. It'll change with new units in Neon Messiah being revealed.
Lien isn't a Seeker but she still makes Legion fast as hell. I can't think of another good Seeker Grade 1 at the moment except the Kay clone. Movie Summary Spoilers stated Aichi is riding Marron so he might be a Seeker and hopefully Soul Blasts. Alfred + Gildas makes a hilarious quick swarm since you can use Alfred's Especial call and then Legion and then use File. Hopefully we'll get a Lemonade clone this booster. Blaster Blade is a tech for a quick important retire or even an endgame retire shot for a last relegion though it's not the best idea since, again, counterblast heavy. Will probably trade him out for an extra Ars.
Farewell Thing Saver, you will not be missed.
Of course, since classic Royals are my babies, I'll make a guide on this eventually. But I'll wait for the rest of Neon Messiah before that. And I'm gonna be pissed if any one of you try to do it before me. But I'd appreciate some assistance so we can all band together like Royals do and make this beast of a king a worthy deck.