This post is paraphrased from Keys to the Japanese Heart + Soul, an excerpt from Japan: An Illustrated Encyclopedia with additional input from Wikipedia.
Ninjou, Natural Feelings
Ninjou broadly refers to universal feelings of love, affection, pity, sympathy, sorrow, and the like, which one "naturally" feels towards others, as in relations between parent and child or between lovers. This can compliment or conflict with ideas of giri, as one's natural feeling towards a person may not align with the obligations the person is bound to. The most clear cases of ninjou tend to arise during conflict, as that is the moment when a person realizes 'true feelings' and must make decisions.
According to Doi Takeo, the Japanese concept of ninjou is the art of knowing how to amaeru (depend on others) and how to respond to the call of amae (short form of amaeru) in others. Giri (social obligations) exist to be pervaded by ninjou.
"The classic example of ninjo is that of a samurai
who falls in love with an unacceptable partner (perhaps somebody of low
social class or somebody of an enemy clan). As a loyal member of his
clan, he then becomes torn between the obligation to his feudal lord and
to his personal feelings, with the only possible resolution being shinjū or double love-suicide. The correspondence to William Shakespeare's play Romeo and Juliet or the Aeneid would be made by Japanese and non-Japanese alike." - Wikipedia
Some people tie the concept of giri and ninjou to concepts of nihonjinron, as they are culture-specific terms. However, there is obvious reason to disagree with the idea that only Japanese can feel a sense of indebtedness, obligation, or of 'normal' human emotions, or that they feel these things more than anyone else in the world does. Although, I do sometimes wish we Americans as a whole felt a sense of giri. We certainly have enough ninjou. :P
Previously: Giri, Reciprocal Obligations
Next: Amae, Dependency Wishes