If multiple chapter abilities trigger at the same time, their controller puts them on the stack in any order. If any of them require targets, those targets are chosen as you put the abilities on the stack, before any of those abilities resolve.

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.

Each symbol on the left of a Saga’s text box represents a chapter ability. A chapter ability is a triggered ability that triggers when a lore counter that is put on the Saga causes the number of lore counters on the Saga to become equal to or greater than the ability’s chapter number. Chapter abilities are put onto the stack and may be responded to.

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.

Removing lore counters won’t cause a previous chapter ability to trigger. If lore counters are removed from a Saga, the appropriate chapter abilities will trigger again when the Saga receives more lore counters.

A chapter ability doesn’t trigger if a lore counter is put on a Saga that already had a number of lore counters greater than or equal to that chapter’s number. For example, the third lore counter put on a Saga causes the chapter III ability to trigger, but chapters I and II won’t trigger again.

The creature card put onto the battlefield by the chapter III ability will enter the battlefield as a flying Angel Warrior (in addition to whatever other creature types it has).

If the chosen creature isn’t on the battlefield at the time damage would be dealt to creatures you control, that damage is dealt to whichever creature(s) it was supposed to be dealt to. It won’t be redirected.

Once a chapter ability has triggered, the ability on the stack won’t be affected if the Saga gains or loses counters, or if it leaves the battlefield.

The chapter I/II ability doesn’t change whether the damage is combat damage or not. If combat damage would be dealt to a creature you control, the damage that’s dealt instead to the chosen creature is still combat damage.

You choose a creature for the chapter I/II ability as that ability resolves.

If another player gains control of the chosen creature after the chapter I/II ability resolves but before your next turn, damage that would be dealt to creatures you control will still be dealt to that creature instead.