The submission path has nothing to do with BDSM in fact, it's classified as such but what's happening here has absolutely nothing consensual.
The MC and his sister have fallen in a trap, they are slaves nothing more.
But even if you choose the dom path you stay a slave, a slightly rebellious slave but a slave anyway!
The best you can expect is becoming like Anja.
Maybe the game will offer the player an end where he will escape with his sister but it would be annoying!
All the pleasure in this game is the sensation to be in a trap with no escape, it's weird but it gives you a strange feeling of loneliness and dispair!