[1] The battle ends when either Kiryu's health gets below 50% or if you defeat Marume.

[2] You encounter the reinforcements when you reach the first room.

[3] When you defeat the initial enemies, the first wave of reinforcements will arrive. When you defeat all of these, the second wave of reinforcements will arrive. Finally, it's possible to encounter a third wave of reinforcements when you go back after entering the area with the dirt floor (area when you split up with Majima).

[4] The intial encounter takes place immediately after leaving the dirt floor area (after splitting with Majima). You encounter the reinforcements when you proceed to the next room.

[1] Reinforcements arrive when you get down to 2 of the initial enemies

[1] When you get down to 4 intial enemies, the first wave of reinforcements arrive. When you get down to 4 again after that, the second wave arrives.

[2] Reinforcements 1 arrive when you get to the bottom of the bridge. Reinforcements 2 appear when you go up at the branching road. Reinforcements 3 show up after you deal with Reinforcements 2. When you go down at the branching road, you'll find Reinforcements 4, followed by Reinforcements 5. Reinforcements 6 appear when you get to the last bit of the area.

[1] Reinforcements start showing up one by one once you get down to 4 guys.

[2] The archer types only appear on the opposite walkway.

[1] When you get down to 5 enemies, the reinforcements will start showing up one at a time.

[2] It is possible to avoid all these fights.

[3] Gion Toji will summon 2 waves of reinforcements during the fight. If you defeat Gion the battle ends, even if there are still other enemies.

[1] When you get down to 4 enemies, reinforcements 1 will start showing up one at a time. Reinforcements 2 show up when you get a QTE during the battle.

[2] When you get down to 4 enemies, the reinforcements will start showing up one at a time.

[1] Reinforcements arrive when the swordsmaster enemy type gets down to less than 50% health.