Oh yeah forgot to tell you, there's also some mystery on the train. For example, later on:

I find Broken Boy rather unique xD. There aren't many BL's with dark concept. And the author did it soo well that many people were traumatized, but are curious to see what will happen next. I feel like the author just go like "yeah lets make this story fvck*ed up and lets not hold back", and i loved it. But of course, this kind of story should not be normalized at all.

It's bascially he's climbing up the train class (from economy to the first) by literally being an onahole for everyone so he can get his marble/pearl back from the red haired dude