adverb
certainly; by all means; absolutely
Emphatic reduplication of 是非, used to strongly express a desire or invitation. Often used when inviting someone or expressing strong personal intention.
ぜひぜひ遊びに来てください。
Please, by all means, come and visit.
その本、ぜひぜひ読んでみたいです。
I'd absolutely love to read that book.