Medicine
Very carefully, Chopper ground the herbs, added methanol and started to heat the mix to distil the essential oils of the herbs. While waiting for the extraction process to begin, he pulled out another thick book, hoping to find a clue to the mysterious illness which plagued his captain nowadays.
Because Chopper refused to let Luffy die!
He would find out what it was, and he would heal him.
He would find the medicine he needed to rescue his captain.
His friend.
The one person who gave him – a being neither animal nor human – a place to call home.