For Lotus:

1. Build the Crypt of Brothers
2. Summon Brother Lythis
3. Select him and press F on your keyboard
4. Attack him to the edge of the water or tree
5. Summon Brother Tausil to help Lythis (just do the same steps.)

For Serpent:

1. Train Ronin/s into a Metal shop and they'll learn Yin Blade
2. Select him and press F on your keyboard
3. Attack him to the edge of the water or tree
4. Select his battle gear by clicking on it or by pressing B
5. If his stamina drained up, simply stop him and if he recovered his stamina, do it again !

Note: Make sure the Ronin/s are attacking before activating the Yin Blade Battle Gear !