Im at chapter 12 i think, its normal to lose one carácter since chp. 9/10? they always kill them at the end, one of those bow units kill in an instant , i lost the red haired pegasus hoshido girl
Bows have bonus damage against
You can get through without losing anyone, you just need to plan.
Keep Sky Knights away from archers, and possibly paired up as the back unit (so they don't get attacked).