esoteric -
adjective -
very unusual and understood or liked by only a small number of people, especially those with special knowledge:
He has an esoteric collection of old toys and games.
esoteric taste.
She has a somewhat esoteric taste in clothes.

necessity -
noun -
the need for something:
You can come early if you want to, but there's no necessity for it.
Is there any necessity to reply to her letter?