Tokyo Babylon is kinda like XXXHolics, weird things happen to people, and whether or not the problem is resolved at the end, there remains to be a lesson to be learned from it. Most of these lessons display the corruption and hypocrisy all over modern society. Take Hokuto, for example, there's one time when she says, "Whenever people see a tree being chopped down, they'll always say something like, 'It's so sad, it's so sad...'. But, take a look for yourself, everyone's still buying tons of newspapers and magazines and hairsprays that are killing the environment."
Or Seishirou with his comments about the evanescence of pop culture, "You know, back then, the Tokyo Tower used to show those delicate and adorable porcelain dolls, but now, they are all replaced by pictures of Madonna and Michael Jackson..."
So, the main theme of Tokyo Babylon links to X: Looking at so many corruptions and destructions, does our society still deserve to live on?
Furthermore...
There has been constant debates about why Seishirou betrayed Subaru ages ago among Taiwan fans.
Here are some of the things they've come up...
1. Seishirou is not evil, just a lot of pride. When he takes the blow for Subaru and lost his right eye, it shows that Subaru has become the most important thing in Seishirou's life. However, he doesn't want to admit that he has lost the bet (it's the pride that kicks in), so he lied about Subaru losing the bet.
2. This is also similar to speculation 1, the only difference is that instead of being filled with pride, Seishirou knew that Subaru belongs to the Sumeragi Estate, which makes Subaru his mortal enemy. He's afraid that Subaru will listen to the grandmother and leaves him once Subaru knows who he really is, so he lied about Subaru not having any significance in his life.
Another thing, it has been confirmed that Seishirou's favorite hobby is breaking glasses. I think it's because after he killed his mom, he wants to force himself to believe that he has no feelings of sorrow, so he breaks glasses and mirrors to numb himself as a reminder that glasses and human lives are equally fragile, and since there's no need to feel sorry for broken glass, there's no need to feel sorry for a dead man.
This is MY speculation, however:
I think, deep down, Seishirou is just another person who is unwilling to see the "good side" of himself, even though he's aware of it, and that he approaches Subaru because Subaru is someone Seishirou believes to never be able to become yet yearns to be. However, Subaru (in my opinion, anyway), is no more than a puppet doing things that OTHER people want, and that disappoints Seishirou, A LOT. Bottom line, I still thinks Subaru is the one who lost the bet.
But, it's up to you to believe who really lost the bet.