Jirōmaru has the appearance of an average kappa, having light green skin with light yellow patches on his stomach area and around his beak-like mouth, pointy ears and webbed hands. On top of his head is a glossy light blue plates surrounded by short green hair. He has thin green eyebrows over his eyes, which have black pupils and does not appear to have discernible sclerae. His shell on his back has a green and light green camouflage pattern, with light brown marginal scutes for its edges. Like his fellow kappas he wears only a vest, his being light yellow in color. While working in Gōhara's company, he wore a long-sleeved light yellow suit, a white collared shirt underneath it, no pants, a red tie and a pair of circle-framed glasses.
Four Generals of Jigoku Arc
Jirōmaru and the kappas of Tono Mountain aid Kitarō and friends in revealing the grave of Chihaya, the lover of Ibukimaru. Together they swim in the lake, creating a vortex that shows the Kidō the grave and allowing him to let his lover rest in peace.