Lesson 540 is the 540th chapter of the Gintama series.
In the past, enraged at the sight of his family's death, Sasaki intended to kill Mukuro, who then understood Shouyou's lesson to her and cried for her actions. She asked Sasaki to cut her down, yet he refused, claiming that what he had to cut down was the current era for its barbarity and himself for being unable to protect anyone. Sparing her life, he requested her to kill him when the time comes as his own revenge.
After the tragedy, Sasaki served the Hitotsubashi Faction, conspired with the Jouishishi and brought down the Tokugawa Family's reign, all of which was to ignite a revolution against the new regime and the Tendoshuu. Noting how Sasaki made himself the populace's enemy, Oboro stated that his enemy was himself.
Nevertheless, the Tendoshuu had looked through his plan and sent the Naraku to the island, intending to slaughter everyone there, thus ending the revolution. The Naraku's fleet attacked the forest instantly, and an injured Sasaki ordered all of the Mimawarigumi to fight back.
Watching enemies and allies destroying each other, Okita questioned Nobume if she was going to let Sasaki end the country along with himself, which she claimed to be her duty. She then recalled how Sasaki spared her life as well as his request and cried at the scene. Suddenly, Kagura jumped in and stopped the duel between Okita and Nobume.
- Sakata Gintoki
- Takasugi Shinsuke (flashback)
- Tokugawa Sada Sada (flashback)
- Hijikata Toushirou
- Sasaki Isaburo
- Hitotsubashi Nobu Nobu (flashback)
- Okita Sougo
- Imai Nobume
- Yoshida Shouyou (flashback)
- Sasaki Isaburo: Dear me. Even being a villain is quite hard work. There are enemies everywhere. It doesn't look like that anyone will become email buddies with me now. Very well. An elite does both good deeds and evil deeds in an elite manner. I, the demon king Sasaki Isaburo, will take every one of them on together.
- Sasaki Isaburo: (To Mukuro) ...If you want to be cut down, then I will not do it. What I have to cut down is this era wheresuch acts of barbarity are commited in this country. And... myself that could not protect anything from that era... Keep using that sword for my sake. And when the time comes, use that sword to cut me down. That is my revenge.
- Imai Nobume: (Referring to killing Sasaki) ...Yes, that's my duty. Even after taking everything from Isaburo, he could not slay me. I ended up living much longer. My final duty is that this time, I will do the slaying. I will... put an end to that person for him.