Of you skipped Quiyuan when he 1st released. Unfortunately for you but happily for me (I got him) you will need to get him in order to bring the most out of Sigrika (Next aero dps) She might be a Echoes skill dps, which means you need our lord Qiuyan to work.
I can read one of u go like " Holy yap fest just do the guide! "
And I say alright people here's the builds.
You can see the pictures above but clearly what u need to know is that Qiuyuan is a great buffer, his crit dmg buff depends on his crit rate you want hik to have 70 crit rate to u lock all his potential buffs (crit dmg, aero dmg, echoe skill dmg, etc...)
He has his own set but he can rock a Moonlit clouds. For weapons you want his sig for bonus buffs+ crit rate, if sig you want 4 cost crit dmg, 3 costs (attack& aero dmg) or (aero dmg ×2) if u want his personal dmg to be higher get his s3, in s0 he's a basic support with quick time on field.
His sig is good for buffs and all not a must you can use any other crit based weapon on him kinda fine.
Hope I helped u if u have q/ ask them in comments below.
Cheers