Ashes of War (Elden Ring)

You can - you put the ashes of war on both weapons and use the right one as usual, and the left one will need to be taken in 2 hands, and only then apply its ability. So you can apply 2 charms like seppuku - you get the left weapon in 2 hands, use the skill, take it back in 1 hand and use the skill on the right weapon.