It is a powerful genjutsu that generates a fluttering rain of sleep-inducing, illusory white feathers. Whomever sees them as they fall, piling up and covering the whole target area, will experience Eden-like bliss and fall into a state of tranquil slumber. No matter how much one resists the hypnotic spell, the desire to sleep is instinctive, and there's no fighting it. However, an experienced shinobi will be able to dispel the genjutsu before it takes effect.
In Buddhism, Nirvana is the complete state of peace, freedom from suffering and detachment from everything in the material world. It is known as the highest point of meditation, which is likely a reference to the technique effect as the target sleeps deeply.