Tengen isnt mean...not one bit. He puts up an act to keep people from getting close. He is super kind with his wives, he really really likes to show them as much affection as possible. He's like...dip shit with affection. Same with Rengoku. He really likes to spend time with him.
But, he is really mean to people to keep them away. He knew when he met Kanroji she hated her uniform. So, as soon as she got close he started commenting on it. She immediately backed off, and they had a lot of probelms with eachother. But eventually Tengen did apologize and they got somewhat close.
With Rengoku he simply...couldn't be mean to him. Rengoku somewhat reminded him of his youngest siblings. They were so bright and happy even when the work was horrible. So, he unintentionally let him get close because he didnt force him away. And soon enough, they became really really close.
