I never manage to extend it unu

(1/2) Basically you just wanna use Elma until you get winged viper for your MC. Equip her with a lot of TP boosting gear (max TP up and melee/ranged TP up is best) and use Blood Sacrifice and Primer to get a lot of TP until you reach 4000.

(2/2) Then use OD and GF and let Primer and BS reach their 3rd cooldown. Use Electric Surge for consistent critical hits, Primer for TP/critical power, BS to farm TP/make ES stronger, GF for Decoy, and Shadowstrike/Early Bird to increase your OD count and stagger foes/buff you.