こいのぼる (Koinoboru) is the pen-name of a Japanese game designer 住吉 伸彦 (Nobuhiko Sumiyoshi) from Hiroshima.
He says he is stuck on tabletop gaming. He organizes a gaming gathering every month, on each 3rd Sunday. He also does activities on introducing tabletop gaming to children.
A note on his pen-name: It appears to be a play on the word Koinobori, which is a carp-streamer; a wind-sock ornament shaped as a carp (koi). This is flown in Japan around the Children's Day, a national holiday. It represents good luck, as the carp battling upstream is like the Oriental dragon climbing the mountain. The baseball team in Hiroshima is the "Hiroshima Carps", so the pen-name incorporates both Hiroshima and good luck.