If you're looking for manga similar to Tetsunagi Kooni, you might like these titles.
Yokai... Japanese spirits. Most people fear them, and a few people even hunt them, thinking they are horrible monsters to be destroyed at all costs. But young Hamachi wants to be friends with them! He sees them as mischievous creatures that could coexist peacefully with humans if only given a chance. When his grandmother dies under mysterious circumstances, Hamachi journeys into the Yokai realm. Along the way, he encounters an ogre who punishes truant children, an angry water spirit, and a talking lantern. Will Hamachi be able to find his grandmother's killer, or will he be lost forever in another world?
Silent and taciturn, a cat demon wanders through the world of humans, encountering creatures as monstrous than desperate.
Seiichi Takamagahara is a high school freshman living alone. One day, he finds a picture book among his grandmother's possessions. The monsters depicted there were not just pictures, but the monsters whose ancestors had sealed long ago. After a long time, the power of the seal weakens, and youkai are released to the world. The reincarnation Seiichi decides to seal the scattered monsters again with the fox god and silver.
Bake youkai, fry youkai, boil youkai, saute youkai. And eat them... The beginning of the youkai gastronomy story.