Eight Gates

The Eight Inner Gates are pure taijutsu: no chakra, paid for with your body.

Controls

Each gate needs a Taijutsu stat. The last two also need their questline (see Quests).

Gate	Needs	Effect
1. Gate of Opening	100 Taijutsu	Power boost, no visible change
2. Gate of Healing	200 Taijutsu	Restores 20% HP once
3. Gate of Life	300 Taijutsu	Crimson skin and bulging veins. HP starts draining
4. Gate of Pain	400 Taijutsu	Bigger boost, faster drain
5. Gate of Limit	500 Taijutsu	Blank white eyes
6. Gate of View	650 Taijutsu	Green chakra cloak
7. Gate of Wonder	800 Taijutsu + Might Guy's questline	Blue sweat-steam cloak
8. Gate of Death	1000 Taijutsu + Might Duy's questline	Crimson flames of boiling blood

The Lee clan starts with +100 Taijutsu.

Questline	Mentor	Needs	Chapters
Gate of Wonder	Might Guy	Level 500+, 800 Taijutsu	Kick the training posts and spar with Lee, Morning Peacock, Front Lotus against the Mist remnants, Kisame
Gate of Death	Might Duy	Gate of Wonder done, level 800+, 1000 Taijutsu	Daytime Tiger, the Zetsu army, Evening Elephant, Madara Uchiha

From the 3rd gate your body tears itself apart. HP drains, and faster with each gate.
The gates close by themselves before they can kill you, except the 8th. It burns for at most 30 seconds, then leaves you collapsed at 1 heart.
Closing the gates leaves you exhausted, with a cooldown based on the highest gate you reached.

Each technique needs its gate open. They're in Extras > Taijutsu and cost no chakra.