Demon negotiation is a critical aspect of Shin Megami Tensei V. You cannot proceed with the game without negotiation partnerships from enemy demons. While your first few negotiations may have gone well, the demons after the first Abscess become a lot more finicky. While there is no 100% guaranteed way to always choose the right answers, we do have some tips for you to lean the scales in your favor.
First, always keep a variety of items on hand. Even if you think you may never need Life Stones or Medicines again, you never know when a demon will request it. Second, take the demon’s family into consideration with choosing an answer. Brutes, for example, will lean towards answers that make you seem tougher, while Jirae will lean towards more playful answers. This isn’t foolproof, however, as sometimes the negotiation will fail regardless of what you pick.
Finally, aim to attack your target demon during a Full Moon. Again, while not always foolproof, sometimes the Full Moon will make your target excessively happy — to the point where negotiation can be skipped almost entirely, and you simply have to pay the fee to have them join you.
One more note — if you negotiate with a demon that you already have in your stock, the target demon will instead grant you Macca or items. This is a handy way to avoid unnecessary battles, as a completed negotiation will always end the battle immediately.