Everyone talking about the one ignorant incest kiss, like we didn't see that in Star Wars. Most would file that under "Oops," and move on unbothered.
Let's review and rate the events of this chapter on the rage scale:
1) Your father, who only visited once a month, is dead. Also you were the second family. There's a
real family, and you ain't it. 10/10 rage points.
2) Teenage angst, this brat ditches his (de facto single)mother on the worst day of her life. 10/10 Rage points! Your poor mother!
3) Goes on an exciting motorcycle adventure with a cute girl, they flirt, she even gives you a coquettish kiss! Oops, she's your sister. 5/10 rage points. It was actually a pretty good road trip, even if it didn't work out.
4) Surprise, now you both live in the mansion with the
real family who hates your guts. But at least you live in a mansion now. Besides, plenty of people in smaller houses also hate their family. Take what is handed to you. 4/10 rage points.
So the main controversy should be the cheating father and the unfilial son. I wonder how this teen who ditched his heartbroken mother will (or won't) screw everything up.
I think the prediction that his half-sister is also a secret illegitimate child is the most obvious plot twist, so I won't be surprised if it comes to be.
@essensue broke down the evidence for it well. If it doesn't happen, that's probably better. Depends on how they handle it.