Excerpt from the game's Wiki:
"Spending enough time with the Manticore allows you to eventually pursue a relationship with her. To progress, the player can exhaust her dialog, encounter her at the glory holes, defeat her in battle by making her orgasm through vaginal sex, repeatedly feed her, and use Manticore Spikes on himself. Over time, this causes you to develop an addiction to her venom, once she learns of it…" jackpot.
Won't spoil the rest.