1. Get yourself a Kunoichi (2000 soulstones).
2. Obtain and equip Rise and Fall, Reactive Shield, Mirror, Avoid Trap, Frenzy (You can switch Reactive Shield with another effects if you want).
3. Obtain Low Temperature contract (Erratic Evolution = HP equals DEX; Afterimage +2 = evasion grants Invincibilty; Tracking = ignore opponent's avoid and parry), you can earn it from shop for 2000 Dried Leaf

You're going with full DEX build so switch INT based skills with DEX skills.
Key stats are simple, just increase your amount of HP and Shield. The higher your HP, the more bonkers your damage will be (only true if you have Erratic Evolution)

Kunoichi's Smokescreen will provide you with Avoid (to proc the Invincibility from Afterimage +2) and Critical.
Frenzy doubles your damage AND HP, to maximize the overall damage; Rise and Fall with amplify it further as long as your shield is still up.
Mirror to prevent getting killed by reflect damage, Avoid Trap to prevent reduction to Max HP and Degradation

Confusion from Frenzy won't be a problem since you'll have 95% Avoidance + Invincibility
Your damage will not be limited by damage limit when it hits critical (you still need Limit Break to break the 9999 HP limit, or you can use HP Boost), but Limit Break is still crucial.

You can just run with no Legendary equipments as long as you increase you Max HP and Shield.
DO NOT accidentally pick any kind of equipment with Spirit Body skill, as your HP will be set to 1.
But if you can get yourself Kamui, you'll be as overpowered as you can be (DEX+, Max HP +, Limit Break +2)

Watch as your Kunoichi inflicts thousands and millions of damage easily while avoiding any kind of harm, and since your Kunoichi is fully set to 100% Confusion, you basically just let your character plays by itself, you'll only need to pick rooms.

Even if you don't have Erratic Evolution, this build is still pretty powerful since Frenzy and Rise and Fall will give you enormous damage, as long as your DEX is high enough.

1. Rise and Fall is optional if you haven't obtained it yet
2. Reactive Shield is needed to make sure that your shield will always be up, since Rise and Fall reduce your power when you have no shield.
2. If you don't have Low Temperature you can opt for Afterimage contract. Look for White Fur legendary item (Armor slot, it has Erratic Evolution, DEX+. Max HP+, and Limit Break while in-game to get the Erratic Evolution effect.