I have a theory. My theory is that the names of theological demons were all invented (this is not a theory, but true) by monks and theologians with a little spare time on their hands. They started with A and worked their way down. This is why we have so man "A" demons but almost no "Y" ones. ;)
I know that theory has a lot of holes in it. But the data remains. I think I could have posted an "A" demon every day. Y on the other hand doesn't give me a lot of choices.
The yakṣa or yaksha is nature spirit from Hindu, Jain and Buddhist literature/myth. They can either be good (or least inoffensive) or evil. There also seems to be a difference between the male yaksha and the female yakṣiṇīs or yakshini. They share a relationship with the Rakshasa.
I had mentioned previously that myths and folklore rarely conform to the needs of any RPG. In D&D terms the yaksha might be demons or even something like faeries. There are numerous stories featuring these creatures, giving them the rough feel to me as fae.
Armor Class: 5 
Hit Dice: 4d8+12* (30 hp)
No. of Attacks: 1 by weapon (long sword) or spell
Special: immune to fear
No. Appearing: 1
Saves As: Fighter 5
Alignment: See Below
XP: 550 / 650
The male Yaksha is a demonic creature related to the more powerful Rakshasa. They appear as very tall humans with large tusks protruding from their lower jaw. There is a claim that their eyes are one fire, but that is due to the orange/yellow coloring. The Yaksha are very strong (18 str) and good fighters. They are typically armed with a large curved blade. Yaksha are almost always evil, though cases have been recorded of non-evil individuals. Scholars have attempted to find a relationship between these creatures and the Oni.
Yakshini are the females of the Yaksha race. They are very, very rare and in fact only 66 are known to exist. Unlike their ogre like male counterpart the Yakshini are human looking. They do not attack with weapons but rather rely on spells. They can cast spells as a 4th level witch. They are typically good (Law) in alignment.
Yakaha will not attack humans, if if ordered so by a Rakshasa if a Yakshini is present. Rakshasas will seek out Yakshini as brides or consorts when possible.