Board Thread:Questions and Answers/@comment-33569516-20200226050125/@comment-27045866-20200226143436

Also from encyclopedia 1

"It is also possible for monsters that use spirit energy as their main source of nourishment to gain nutrients from eating ordinary food, but it is comparatively far less efficient. On the contrary, it is also possible for those monsters that mainly eat ordinary food to take in spirit energy as their own demonic energy. A man's spirit energy is delicious and appealing to all monsters. It is their number one treat."

All monster regardless of type, age, or marital status can eat food to sustain themselves through food but it's less efficient. It's through sex with a person they love that both the man and monster receive more energy back than they put in, creating a power spiral of infinite energy.

And from World Guide 3

Pretty much all bodily fluids contain essence, which is just the word for the mana of men and mana is just life energy.

"All living things have the power to produce mana, which is vital energy, within their own bodies. Mana is always constantly being produced, and when old mana is swapped for new mana, the old mana is naturally released outside the body into the surroundings. Men's semen, saliva, sweat, etc., contain mana, but the quality of each is different, and they also taste differently to monsters. Out of all of these, semen contains the largest amount of freshly produced mana, which tastes the richest and is the most nutritious."