Pre-place the exit tunnel before you trade, then use burrowed Q into knockup for a short hit-and-run and treat fury on the wave as part of the combo, because Rek'Sai top gets stronger by healing the trade back rather than forcing every turn into a max-fury bite
Rek'Sai is unusually good at living in the messy middle of top lane, where even or slightly losing 10-minute states are still fine if they keep your health, fury rhythm, and component timing intact, but delayed components are where the champion's results really fall off
When you get ahead, leave a real tunnel web in the side lane and use Void Rush as the commit, finish, or dodge after contact is already won, because Rek'Sai's early leads lose a lot of force once the game stretches out and she stops dictating how long each fight lasts
Bite when the trade is already yours, not when you are still trying to make it yours. If unburrow plus Q autos got their answer spell out, or they are stuck close enough that the fury E ends the exchange before they can turn it, take it. If the lane is still open and using E would keep you in range of their longer trade, skip the greedy finish, tunnel out, heal on the wave, and run the pattern again on the next window. Rek'Sai top gets more from two clean bites across two turns than from one forced bite that loses the lane back.
Rek'Sai generates Fury by Attacking and hitting with basic Abilities. She consumes this Fury while Burrowed to restore health.
Rek'Sai's next 3 basic attacks deal bonus Physical Damage to nearby enemies.While Burrowed, Rek'Sai launches a burst of void-charged earth that damages and reveals enemies hit.
Rek'Sai burrows into the ground, gaining new abilities and increased Move Speed. Her vision range is reduced and she cannot use basic attacks.While Burrowed, Rek'Sai may cast Unburrow to knock up and damage nearby enemies.
Rek'Sai bites her target, dealing physical damage, or bonus true damage if she has max Fury.While Burrowed, Rek'Sai creates a re-usable, long lasting tunnel. Enemies can destroy it by standing on top of either entrance.
Rek'Sai passively marks targets by damaging them. She can activate this ability to become briefly untargetable and lunge at a marked target for heavy damage based on their maximum health.