I knew it, his original owner found herself in a situation where she couldn't keep taking care of him. I thought this woman was just a friend, but she was in fact the younger sister of Kotetsu's original owner.
"Selfish circumstances"
Taking care of one's parents is selfish? Bro just doubled down and it's actually painful to see... he may have gained a human form, but in the end he's mentally still the same old grumpy cat he used to be.
He's lucky he's surrounded by actually kind people. Komugi is figuratively his and Honami's angel, sent down from heaven to make them happy.