He has short hair and has a seaweed over his head.
He had a crush on a girl named Nagisa, but was too shy and ended up playing a prank on her, by making her wear a necklace made of sea shells from garbage. He tried to make up for it, by making a proper shell necklace for her, but he drowned at the beach while collecting sea shells. His spirit lingered however at the beach, and he finished the necklace and gave it to Nagisa who accepted it, but he dragged her into the sea as he was still shy. He would continuously make shell necklaces for her only to lose them, and ends up forgetting his lingering attachment. As a result, any girl close to his age would be able to see him, and would be dragged into the sea if they receive a shell necklace from him.
3 years ago, he met Sakura, who figured he would try to pull her out to sea, and he promised her a shell necklace, but she ran out of time and had to go home.
He sent a letter to Sakura, saying he’ll give her what he promised, so she came back to the beach with Rinne and Tsubasa, but as usual he lost the shell necklace. He eventually gets to remember about Nagisa, and Rinne figures he had to speak to her to pass on, so he used a special wick to create a replica of young Nagisa made of sand, and Satoru learned from her that she collected every shell necklace he made that washed up on shore, and so happily passed on.