Fake Difficulty: Getting trapped into a series of inescapable attacks, running into the Boss in Mook Clothing when there's no respawning goons around to pound on to recover HP, and getting lost in Chapters 3 and 4 then getting killed only to be forced to start the entire Chapter over may not be anyone's idea of fun.
Soray at the end of Chapter 5 is considered one of the hardest bosses of the game. To elaborate, during the second phase of the battle he sends out four spear-like projectiles that spins and zero-in on Yunou location. This does doesn't seem like a problem at first, but that's only a warning of what's to come for the third phase. Once the battles into phase 3, that's when it gets worse since he will spam those things almost non-stop, and those things can trap Yunou while spinning around and dealing damage to her. Now imagine 8 or more of those things traping poor Yunou as she helplessly takes damage while Soray sicks even more at her.
Kurow in Chapter 4 can be considered as such as well being also a Wake Up Call Boss. He uses powerful magic attacks, projectiles that will build up Yunou's CP gauge to force a Magic Leak Burst to cut her HP in half (unless her Max CP is greater than her CP Limit), and the player have to fight him on ground while he's free to fly the entire time.
The penultimate battle with Elshiria and Narju in Chapter 6. Elshiria specializes on Beam Spam that not only hurt, but are also unblockable. Adding to that are her Bullet Spam and Homing Projectile attacks that are both annoying and painful, and she really doesn't play nice halfway into her second phase of the battle. Narju on the other hand, her ice magic seems to gone Up to Eleven since the player last fought her in Chapter 2. Some of new attacks include a Bullet Hell barrage of icicles, homing shots that explode into huge icicles, and surrounding herself with huge chucks of ice that can also trap the player into painful attacks.