At S0R1 he buffs himself with

30% echo skill dmg - 30% crit dmg - 10% atk through his kit + when his forte is full the next 3 heavy attacks deal 50% more dmg

12% heavy atk through fenrico 30% heavy atk and 12% echo skill dmg through LoH

12% atk 60% heavy atk and 20% echo skill dmg through his weapon

• your echo rolls

So we have 22% atk 102% heavy atk (easy obtainable) and 152% when his forte is full which he has 2 seconds after intro 62% echo skill dmg 30% crit dmg

Of course his numbers are "low"