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
50.0%
(-0.5%)
46.4%
(-1.1%)
1.1%
(+0.1%)
2.0%
(+0.7%)
576
(-21)
