The control-change effect of the third chapter ability lasts indefinitely. It doesn’t wear off during the cleanup step. In a multiplayer game, it does expire if you leave the game.

Any nonland permanents that come under the target player’s control after the second chapter ability resolves will untap as normal.

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 lore counters.

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.

Nonland permanents target opponent controls that are already tapped when the second chapter ability resolves won’t be tapped again, but they won’t untap during their controller’s next untap step.

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.

The second chapter ability targets the player but not their permanents. Permanents with hexproof may be tapped this way.

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.

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 III chapter ability to trigger, but I and II won’t trigger again.

The second chapter ability keeps the permanents tapped even if Kiora Bests the Sea God leaves the battlefield before that player’s next untap step.

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.