Rek'Sai should leverage her very high early game pressure and fast clears to invade and disrupt Jarvan IV before he can set up his engage tools.
Prioritize aggressive pathing and river control to deny Jarvan IV the tempo advantage from his strong early ganks and objective setups.
Jungle Plan
Use tunnels to create unpredictable gank angles and pressure flashless or immobile lanes before Jarvan IV completes his first clear.
Track Jarvan IV's pathing closely and counter-gank his early river moves to punish his medium dueling and invade resistance.
Prioritize early dragon and Rift Herald control by leveraging superior clear speed and early numbers advantages to deny Jarvan IV scaling and objective access.
Danger windows
Be cautious during Jarvan IV's level 2-3 gank attempts when (E)+(Q) is ready and lanes are overextended or lack flash.
Avoid isolated river fights or objective setups when (R) is available to trap and lock down Rek'Sai.
Watch for forced smite fights on dragon or Herald where Jarvan IV's engage and frontline utility can overwhelm Rek'Sai if caught out of position.
Early game
Start with a three-camp clear into an early invade or counter-gank to capitalize on Rek'Sai's high early pressure and Jarvan IV's medium invade resistance.
Fight for first Scuttle when nearby lanes have priority to secure vision and deny Jarvan IV early objective control.
Avoid extended fights if (E)+(Q) engage combo is up and lanes lack flash, as he can force early flashes and repeat ganks.
Power spikes
Rek'Sai spikes at level 3 with access to her full kit and tunnel mobility; use this to invade or gank before Jarvan IV finishes his first clear.
Respect Jarvan IV's level 2-3 window when (E)+(Q) is available, as his long-range engage can force early summoner spells.
Respect Jarvan IV's level 6 spike with (R) lockdown; avoid isolated fights near objectives without vision to prevent being trapped.
Win conditions
Convert early tunnel ganks and invades into lane priority leads and objective control before Jarvan IV can stabilize.
Use superior clear speed and map mobility to contest Scuttle and invade safely, denying Jarvan IV farm and tempo.
Exploit Jarvan IV's medium dueling by forcing skirmishes when his engage combo is down and collapsing with lanes to secure kills and objectives.
Tip: For Rek'Sai vs Jarvan IV, read overview, trading pattern, and danger windows first for a fast Jungle lane check.
