Manipulation
From Neverend
By doing something an NPC doesn't like, they will try to avoid you and try to avoid that activity more. By convincing them that they do like it, they will welcome the action in the future. This could be used to make NPCs enjoy certain activities, such as wearing no top, bottom, or underwear, while feeling perfectly normal. The NPC would have such as positive experience to wearing less clothes that they would hate wearing more clothes. This could be taken further to include sex, sex in public, bondage, pain, inflicting pain, entering combat, competing, fighting, etc.
The NPC would also welcome the player who has given them the most positive response so far, and submit to actions including agreeing to do specific actions, travelling or partying with them, or getting discounts or special information.
This can also extend to slaves, servants, employees, pets, familiars, etc. Teaching a dog to enjoy combat will cause it to attack more than a dog who dislikes combat and tends to run away. Teaching a dog to fetch or do tricks will make it enjoy that activity over a lazy dog.
NPCs with a strong will or with very strong inner goals will be too hard to change their minds usually. Someone who will always be loyal to a certain town, group, religion etc or has very strict ideals about sex and nudity will be able to resist and persuasion. Characters who are middle ground or neutral can be turned either way.
NPCs may only obey the players they are most loyal to, so a bunch of guys hitting on a barmaid will be rejected, but someone who has talked to her often, treated her well, and made her smile or be interested in conversation to the point the player is very well trusted by the NPC, and can tell the NPC to lift up her skirt, remove her panties, and have sex in front of the entire city.
A level of strong trust or loyalty takes time, often with multiple visits rather than one "grinding" session of compliments and gifts all at once (this may cause a negative reaction with so much unwanted attention, and the player is trying to hard to change her mind).
Eventually, a character with a strong ideal could be shifted to the other end of the spectrum, but it would take days of earning trust, or forcing a change of view by use of psychic abilities, restraint, torture, spells, magic items and manipulative items.
Changes with the most impact cause the NPC to give up their old way of life, whether its from being a shopkeeper to an adventurer, a princess to a slave, a warrior to a pacifist, or an adventurer to a city dweller.
NPCs who enjoy being party members with a player will interupt their current schedule to party as long as needed. This creates a bond over time of trust and loyalty, especially if they fit the NPC's ideals (not murdering, stealing, etc). The NPC will be more likely to perform requests after this trust is gained, such as performing a valiant action, having sex, or doing something they wouldn't have done with a stranger.
KOTOR shows a good example of how long term trust affects what someone is willing to do. There is a point where you can tell your party member to kill a close friend because of his life bond with you. Besides longterm trust, there is brainwashing and torture to achieve perspective change through negative means.
Every NPC could have basic ideals that are on a scale, determining how they act most of the time. Dialogue and actions allow NPCs to change over time, or strengthen their ideals. It could also turn someone to thievery, exhibitionism, greed, charity, kindness, horniness, honesty, piety, sadism, masochism, cruelty, anger, patience, adventuring, or settling down to live peacefully.
