There are several different species of dangerous animals on it. Boa Hancock openly stated that the island is dangerous even by Kuja standards. A country supposedly used to exist on this island, but its people could not survive against the extreme environment and died out.
Rayleigh spent the first year and a half to teach Luffy the basics of Haki. After Luffy mastered them enough, Rayleigh left him alone for the remaining half year to finish his training. It was during these two years that he developed Gear Fourth to deal with the tougher animals.
After another half a year, Luffy became the "boss" of the island, and even befriended some of the animals (which Luffy partially regretted, since he had missed out on getting to eat them). He departed when the time came to rejoin his crew, picking up his straw hat, with the Kuja Pirates coming to pick him up.
- "Rusukaina" means "Anybody home?".
- ↑ 1.0 1.1 1.2 1.3 1.4 One Piece Manga and Anime — Vol. 61 Chapter 597 (p. 9-19) and Episode 516, Rayleigh takes Luffy to Rusukaina to train him.
- ↑ 2.0 2.1 One Piece Manga and Anime — Vol. 61 Chapter 598 (p. 1-3) and Episode 517, Luffy has successfully conquered the island.
- ↑ One Piece Manga — Vol. 78 Chapter 784 (p. 9), Luffy reveals that he developed Gear Fourth on Rusukaina.