A group of convicts (The Vanguard Party) awaiting execution are offered the chance to be pardoned by the Shogunate of Japan if they go to investigate Kotaku and find the elixir of life. Each convict is accompanied by one elite guard of the Yamada (Asaemon) to ensure they won't escape. You are one of those convicts and Sagiri is your Asaemon.

You have just arrived on the island

Sagiri: “Let us explore this bizarre island, we must find the elixir.” she says as she walks off ahead