Why Onmyoji?
A new class that allows Dark players to do what Runeslayer did, but without the runeweave clicking (no more carpal tunnel).
If you only have 1 opus and it is using the Chain of Falsehood, it can make playing other content miserable as it reduces charge bar gain by 100%.
A solution is by grabbing another Dark Opus (the primal one) and make the other one use Chain of Falsehood, while your main opus uses a more general skill such as Stamina.
Onmyoji has a skill called Celestial Genesis which gives MC full bar and ougi reactivation when 7 seals (unique stacks to the class, starts at 10 and any ougi increases it by 1) are consumed.
No Qilin
Sealing Talisman + Pandemonium > Splitting > Celestial Genesis. This pattern deals more dmg in 3T as you do not need Qilin friend and Sealing Talisman gives MC Tri-strike.
Qilin
Celestial Genesis > Splitting > Qilin > Splitting > Celestial Genesis. Remember than Celestial Genesis only provides full bar when 7 seals are consumed, and your seal is already at 3 at Turn 1.
vs Runeslayer
The grid and example is the same as Runeslayer, only difference is MC skills. The only downside would be that you lose access to another echo source as Runeslayer has Dragonbreak, but you do save yourself from having to deal with runeweave menu.
Sample Grid
Opus 3rd key MUST BE Falsehood (Echo). Seraph can be replaced with Ultima if it's ULB for On Element fights.
For off element fights, you can replace the seraph with anything, most likely more damage mods as you probably would not reach the cap.
If you use skill nuking characters like Bowman and Seox, you can slot in Agonize / Celeste Saber Ater for more skill DMG.