When he was in elementary school, he and 2 of his friends found an abandoned puppy in a park. They named the little dog Bero and would bring him food everyday, since none could bring him to their own home. A Sunday, it was Ken’s turn to bring him food, but his parents took him to an amusement park and he completely forgot about Bero. From the night he got back home up until the next day, it was raining, and Bero had vanished. Although Ken wished to believe Bero was found and adopted, he blamed himself.
When he was recently allowed to own a dog he named Kotaro, the spirit of Bero came, and a rain cloud appeared above his head. When he sought Rinne's help and learned the spirit of a dog is connected, he feared Bero came to loathe him, but it is revealed that Bero was indeed found and adopted by a girl who loved and cared for him. Rinne concluded that by the time Ken adopted Kotaro and felt guilt over leaving Bero out in the rain, he unintentionally drew the spirit of Bero, who passed away the same time, and the rain was a projection of their memory. The spirit of Bero is revealed, putting his paw on his shoulder, forgiving the boy of his burden and passes on. After that, Ken wondered if his dog Kotaro was cursed, but it’s just because he did not train him well.
- He is the only student so far to be of a class 5.
- The 2 Kanjis of his name stand for "Rain" and "Field".
- The Amusement Park he went to was called ◯sneyland (◯ズニーランド), which is obviously Disneyland.