From Eden Eternal Wiki
To enter Sakura Island you need to talk to the the NPC located in Aven <Sakura Island Teleport Agent> Takahanshi (X:313, Y:395)
When you enter you will receive a massive boost to your HP.
This is Sakura Island. This map is open PvP so any player can kill you inside it but members of a party cannot damage each other and are treated like normal as if outside of the Island with each other.
To leave Sakura Island talk to <Aven Teleport Agent> AragakiKaoru (X:272, Y:442)