There are two people with facial paralysis in Heizi's family, one is born and the other is forced.
Kuroko Takuya robbed Kuroko Tetsuya of all his sense of existence in his mother's belly, which became the starting point of his miserable life in the future.
I don't know how long it will take to repay the excessive sense of existence for the thin sense of existence.
But the bond between the twins was doomed from the beginning - so he probably won't be able to repay it in his lifetime.