@Jojeke
Ahh, but she has become his motivation. Shindou prides himself on his work ethic and he needs some monstrous reason to burn himself out continuously. He idolized her, so its not even about the crush/love anymore.
You know what would be cool?
If he had a bit of reflection and noticed that was how HE acted. Be like, "Damn, what an asshole. But wait a minute, I'M sorta like that".
@Murricath
Cuz its Feng Shui, Wuxing, and Taoism. You have your 5 elements that have to be balanced, and this was developed pretty early (and subsequently spread to Korea and Japan)