Mr. Kawamoto is first introduced in a flashback with Marin as the owners of their Inn. About 4 years ago, before the Newspaper Club came to the Human World for a summer vacation and were brought to the Inn by San Otonashi, he and Marin lived together. They were happy that they found some information about the Inn that they built in the local journals. He believed that they'll surely be able to increase their patronage and will become the number one seaside resort. Later that night, he was killed by Fairy Tale's 7th Subdivision Leader, Kanade Kamiya, a Siren who posed as a guest staying for the night in the Inn. Marin saw this tragedy and on how she knew all about yōkai since his death.
About 4 years later after San defeated Kanade, she, along with Marin, continued to make the Inn the best in the sea resort knowing that's what Mr. Kawamoto would've wanted from the beginning.