Seidou was Owl number 15 and of course, number 15 is his token tarot number- The Devil
The ego is the key to understanding the Devil card. Ego tells us we’re better than the other guy, or we’re not good enough for the glee club.
We are designed for greatness, yet when we stoop to the level of ego-thinking we’re blind to our own beauty.
An ego-driven mind is one that operates under the illusion that love and acceptance must be obtained at all cost.
The truth is that love and acceptance can never be gained because they are always ours - they are at the core of our being at all times [x]
This explains Seidou’s character up until the last coupl of chapters. But of course, this 15 is upside down so it corresponds to the reversed meaning of the tarot card:
Which is what Seidou tried to do by killing Tatara and what Amon wants to help him with by saving him. Go Seidou, you break those chains ;~;
There’s also the upright 21 on the nearby tank highlighted:
As such, it embodies the completion of a long, sometimes difficult journey. The World represents all elements coming together in order for us to receive the satisfaction and success for which we’ve been striving.