Tenkai Kumichou, is a the leader of the Tenkai group. He refers to Ryuichiro Kuroda as "Anki" which means older brother. This means they have a senior-junior business relationship in the Yakuza world. He's considered a friend of the Kuroda family and thus, Kumiko has referred to him as "Uncle Tenkai" out of respect. He's always seen with his sunglasses on and never takes them off.
Tenkai is very serious when it comes to Yakuza matters. That aside, he's a bit of a goof. At least to Kumiko's memories, as respectful as she was to him. She has memories of him being a silly drunk sometimes. And he also tends to follow trends to keep him healthy. During a visit, Kumiko noticed all of his members were laughing. Tenkai had been following suggestions of an apparent "guru" who said laughter would help; much to her annoyance.