Take a look at the color painting on page 1.
In this hypothetical game, there's a boy who turns into a dragon. It's due to no fault of his own, but is rather the result of a curse put on his parents by an angry wizard. The people of the land want to kill the boy, for when he takes the form of a dragon, he wreaks destruction.
Yet you know that the only chance of destroying the big boss you must fight at the end of the game is with the help of this boy/dragon, so it's critical that you ensure his safety. During the game, you must lead him across the land. When he's a boy, you need to protect him from those who try to kill him. Yet when he turns into a dragon, he tries to kill you he can't help himself. In those situations, you need to injure or weaken him without killing him. So sometimes you're protecting him, and sometimes you're fighting him.
Other factors make your relationship with him even more complex. In one situation, when he's a dragon, he kills some innocents who don't deserve to die (they weren't even attacking him). Further complexity is added in that, to help you fight the big boss at the end, he is willing to sacrifice himself as penance for the innocents he hurt earlier.
You're likely to have many layers of feelings toward the boy:
A desire to protect him.
Fear of him when he's a dragon.
Pity toward him for being the victim of a curse.
Admiration for his willingness to sacrifice himself to help you kill the big boss.
This would truly be an example of Player Toward NPC Relationship Deepening.
An Example of Technique Stacking
Because the breadth and depth of emotion in a game is heightened when Emotioneering techniques are used in combination, I feel it's always worth pointing out such examples when they occur in some of the hypothetical games described in the book. The game with the boy/dragon employs a few other Emotioneering techniques in addition to Player Toward NPC Relationship Deepening:
Because the boy is the subject of undeserved misfortune, he has NPC Rooting Interest (see Chapter 2.10).
Protecting an NPC and taking responsibility for him causes a player to bond with him, which I call having Chemistry with the NPC. It's a Player Toward NPC Chemistry Technique (see Chapter 2.11).
When the player finds himself protecting the boy, even though the boy, in dragon form, has tried to kill him, and even though, while a dragon, he killed some innocents, this is an Emotionally Complex Situation (see Chapter 2.15).
When the boy is willing to sacrifice himself in penance for the deaths he has caused (even though these were the result of a curse put on his parents), this not only gives him additional Rooting Interest (see Chapter 2.10), but Self-Sacrifice and Wisdom are each techniques that give him depth. They're NPC Deepening Techniques (see Chapter 2.2).
By the end of the game, the player will have truly experienced some emotional and moral complexity. For example, the player will have seen that the boy is right in wanting to live; the villagers are right in wanting to kill him. The boy's willingness to sacrifice himself in the end, to restore his feeling of self-worth and to punish himself for his crimes while in dragon form, could be equally argued to be reasonable and unreasonable. The player's character will be loved by many people in the land for daring to take on the big boss but the player's character will also be despised by others who were victims of the boy when in his dragon form.
Experiencing the emotional and/or moral complexity of a situation, especially when these complexities develop over the course of a game, can leave the player wiser and thus deeper. They're First-Person Deepening Techniques (see Chapter 2.21).