This is only a mere concept/idea and can be tuned up to fit properly in the current meta of CN and EN servers.

Sussano Shisui has been long gone from the meta as it's counterpart (Kimono Shisui) gaps everything Sussano Shisui does and considering 10T Obito got breakthroughs in CN, it should be considered Sussano Shisui needing breakthroughs as his skills are very outdated and don't work well.

Mystery +2: Deals unmissable damage, 4 Combo, Interruption and Suppression Of Super Armor to 12 Enemy Units. The selected unit will suffer from Knockdown and it’s mystery skill locked up to 2 rounds.

Mystery Y+1: Deals unavoidable damage, 12 Combo, Irremovable Chaos and Suppression Of Super Armor until the end of the next round and deals 80% to units 2 grids away from that unit. The selected unit will suffer from Knockdown.

Standard +2: Attacks a random line of enemy units, causing 5 Combo and Irremovable Ignition with a high chance to cause Low Float. This skill ignores a small amount of defense and resistance.

Chase +2: Chase and attack a Repulsed unit, causing High Float, Interruption and Ignition, while increasing Shisui’s Attack and Ninjutsu by 18%. Can be triggered 3 times each round.

Chase Y: Chase and attack a Repulsed unit, causing High Float, Interruption and Ignition, reduces mystery cooldown by 1 Round, while increasing Shisui’s Attack and Ninjutsu by 12%. Can be triggered twice each round.

1st Passive +2: Triggered at the beginning of every even numbered rounds, causing this unit and 1 random ally to enter Lv 2 Explosive Mode . Units in Lv 2 Explosive Mode are immune to debuffs, gain a 10% speed bonus, reduced damage by 30%. Additionally increases chase by 2 times, lasting until the end of the round.

1st Passive Y: Triggered at the beginning of every even numbered rounds, causing this unit and 1 random ally to enter Explosive Mode Y. Units in Explosive Mode Y are immune to debuffs, gain a 60% increase in Critical Rate and heal 40% of ninjutsu deals. Additionally increases chase by 2 times, lasting until the end of the round.

2nd Passive +2: Immune to Low Float, High Float, Repulse, Knockdown, Interruption, reflects all debuffs aimed at Shisui at the start of every round. When receiving an attack, reduce the attacker's critical rate by 60% and ninjutsu by 8% lasting until the end of the round.

2nd Passive Y: Immune to Low Float, High Float, Repulse, Knockdown, reflects all debuffs aimed at Shisui at the start of every round. When receiving an attack, Shisui has a 50% chance to cause Irremovable Chaos.

The concept may not be good but "Irremovable Chaos" would fit Shisui perfectly.