Sukunda decreases one target's accuracy and evasion.
In Shin Megami Tensei: Liberation Dx2, Sukunda decreases the enemy faction's accuracy and evasion by 20% each. The effect lasts for 3 turns.
In Shin Megami Tensei V, Sukunda's effect lasts for 3 turns and can stack twice. Casting Sukunda again before the effect wears off will refresh the turn timer. The icon indicating that Sukunda is active will be blinking the turn before its effect wears off. Sukukaja presumably decreases the target's Accuracy of offensive attacks by 9/10 on the first stage, and to 85/100 on the 2nd. On the other hand, in terms of their evasion, the accuracy of attackers that target the afflicted user are increased to x1.1 on the 1st stage, and x1.2 on the 2nd. If the Accuracy of attacks were to exceed 100% via the buffs, it would simply treat attacks as guaranteed hits.
In Persona 4 and Persona 5, Sukunda lasts for three turns.
In Persona 5 Strikers, Sukunda instead lowers a range of enemies' Critical and Auto-Evasion rate. It lasts for a certain period of time: under default circumstances, it lasts 50 seconds.