The Rek'Sai build for Jungle is Stridebreaker and Conqueror. This LoL Rek'Sai guide for Jungle at Platinum+ on 13.24 includes runes, items, skill order, and counters.
Rek'Sai Counters
48.2%
(-1.8%)
44.5%
(-2.0%)
1.9%
(+0.8%)
4.8%
(+2.9%)
604
(+27)