Hoshigaki have 3 moves and 1 Talent. Water Walking, Water Floor, Dive, and Shark Bomb.

To get Water Walking Talent, talk to a shark then run on water until you get it. The talent allows you to heal on water. [walk/run, you won't get progress on it for standing still]

To get Water Floor, you have to talk to the shark again, then heal HP in combat until you get it. The actual move is a water floor that you can heal HP off of if you run on it sporadically.

To get Dive, you have to wipe one Genin 6 in Permadeath event in order to get the move. It allows you to dive underwater for around 10 seconds and regen HP [due to the talent]. It is recommended you talk to the shark again before doing it.

To get the last move, Shark Bomb, you must wipe one Chunin+ in Permadeath event, and you shall receive it. It spawns a shark projectile that does good damage. It is recommended again that you should talk to the shark before getting the grip.