Viking funeral to release the spirit so it could rejoin as the Sunny. It's the final joiner and the spirit of the Adam tree. It was planned since before One Piece started.

It will be the one to fight Sanjuan after Franky turns the whole ship into a mech but the tree reveals it just wanted to go on one more adventure was actually referring to one more adventure with Joyboy and take over the ship mech with the new reactor that uses sun energy instead of cola and it's own flesh, the Adam wood.