>>531581105
You get 15 coins per Nobukatsu/Anning/ etc whatever 1* servant has a rate up in the fp summon compared to the average 2 from 1*. Basically like 1.73 grails per million FP if you did it outside any 1* fp rate up while you get 2.04 grails worth per 1million if you do it during a 1* rate up.
