Rek'Sai is an early tunnel ganker and snowball fighter who must leverage her high early game pressure against Nunu & Willump's objective control and gank utility.
Focus on invading and contesting camps before Nunu can safely use (Q) sustain and (W) engage angles to threaten lanes and objectives.
Jungle Plan
Use tunnel paths to invade and counter-jungle when Nunu shows on the opposite side or after his early gank attempts.
Contest dragon and Rift Herald setups aggressively after successful ganks to deny Nunu's strong (Q) plus Smite secure.
Track Nunu's pathing and be ready to counter-gank lanes vulnerable to his (W) angles, using your knockup (W) to disrupt his engages.
Danger windows
Respect Nunu's early (W) knockup gank engage from fog; avoid overextending without vision on his approach angles.
Beware isolated river fights where Nunu can chain CC with (W) and (E), especially near contested objectives.
Be cautious contesting objectives when Nunu has lane priority and can start dragon or Herald quickly with (Q) sustain and Smite.
Early game
Start with a three-camp clear into early gank or invade to capitalize on Rek'Sai's fast clear and high early pressure.
Fight for first Scuttle only if nearby lanes have priority to avoid Nunu's (W) surprise engages.
Avoid isolated river fights early where Nunu's (W) knockup and (E) root can punish you without lane support.
Power spikes
Rek'Sai spikes at level 3 with access to tunnels and (W) knockup, enabling early ganks and invades; use this to force plays before Nunu reaches objectives.
Nunu's first dragon or Herald spawn powers his (Q) plus Smite secure; punish his objective starts by pressuring lanes and invading opposite side.
Nunu's level 6 (R) adds zone control; layer your (W) knockup to interrupt or avoid his full channel in skirmishes.
Win conditions
Convert early tunnel ganks and invades into dragon and Rift Herald control to snowball map pressure.
Deny Nunu's free farm and objective setups by invading camps when lanes show on the opposite side.
Use superior dueling and mobility to counter-gank and punish Nunu's overextensions before his utility scales in mid game.
Tip: For Rek'Sai vs Nunu & Willump, read overview, trading pattern, and danger windows first for a fast Jungle lane check.