Firja's Retribution

As a Saga enters the battlefield, its controller puts a lore counter on it. As your precombat main phase begins (immediately after your draw step), you put another lore counter on each Saga you control. Putting a lore counter on a Saga in either of these ways doesn't use the stack.

Once the number of lore counters on a Saga is greater than or equal to the greatest number among its chapter abilities, the Saga's controller sacrifices it as soon as its chapter ability has left the stack, most likely by resolving or being countered. This state-based action doesn't use the stack.

Only Angels you control as the chapter II ability resolves will gain the activated ability. Similarly, only Angels you control as the chapter III ability resolves will gain double strike. In both cases, Angels that come under your control later in the turn won't gain the ability.