Nitori is the first boss of Stage 5. She has 6000HP, and you will be fighting her inside the green egg shaped mech thing she appears in whenever she gives you a shop ticket or is behind her at the store in Stage 1. It mainly attacks with projectiles, either long ones that should be double jumped over, or a large amount of blue energy shots (her most dangerous attack, as they will continue to move in TIME stop). Other than this, she will land and then dash across the ground, which is an ideal time to hit her with a large amount of basic attacks, as she is not invulnerable during this period.
I personally used the Lost Holy Sword for this fight, as the auto attack gets over a lot of the issues with the boss being able to fly, and deals solid DPS. Every time my TIME gauge was full, I would stop time and just stand there letting the sword attack her, then when it ran out, dodge attacks in real time to quickly replenish it, then repeat.
Use Thousand Daggers. It is by far the best option in the game for every single boss bar none
Thousand Daggers is also a very viable option, though you will find youself lacking in MP if you use it in real-time too much (and can only be activated once per TIME stop). You can just pop in and out of stopped time, just spamming the skill. This method will be probably be faster than the one with the Holy Sword (it is the strategy for the Boss Rush after all). It's down to preference which one you want to use