Edit: found something cool, you get a bad end if you try to face the world 1 final boss while you have a stage 2 demon seed parasite inside you. Ends in a nice animated GO screen with hasumi giving birth.
Edit 2: Ok, the houseplant is seriously cool. In addition the the scene you get the first time and the animation you can freely go through after, if you feed it enough it'll evolve to a bigger plant, with its own scene and animations, that absorbs pollution even faster. You can even hit it to make it refund you the pollution it absorbed, and doing it enough will cause it to de-evolve back to base state. Gonna grind some more pollution to see if there's a third stage. Highly recommend getting machine translation if mind control/hypnosis/aphrodisiacs are your thing, cause the scene are pretty hot, theres a sense of "this thing is growing beyond my control", both in the sense it's getting bigger&stronger, and Hasumi is succumbing to the pleasure.