Queen Sangria is a Chessmaster who has been sending powerful monsters against the heroes and staying well out of harm's way. However, she suddenly decides to confront Ichigo herself for the final showdown.
Queen Sangria normally does everything to remain innocent in the eyes of the public. After her actions are put forth to the public causing great amounts of civil unrest, she attacks the heroes instead of trying to scavenge her reputation.
Ichigo needs to fight Queen Sangria alone Because Destiny Says So, and Sangria has found a way to render Budou and Ringo powerless.
Queen Sangria has been steadily gaining power all this time; to become immortal, she has to slay Ichigo with her own hands so she can suck her soul dry and claim the heroine's magic as her own.
Subverted: Queen Sangria acts like an idiot hero to draw Ichigo into her perfect trap...
Double Subverted: But it turns out that the trap is ineffective, forcing Sangria to fight Ichigo anyway.
Parodied: Queen Sangria is hit on the head immediately before the grand finale, causing her to become much dumber than previous.
Zig Zagged: Ichigo and Sangria are both tactical geniuses. But when the climax came around, we lose sight of their ingenuity. In other words, they act like idiots. However, it's actually all part of each plan's to mark the other's downfall. But because their plans contrasted each other, nothing could move, so they had to fight head on anyway. But we soon find out that they don't simply act randomly but in fact forcing their initial plans to work.
The writers want to add drama to the Grand Finale by splitting the team up, even though Ichigo wouldn't normally make such a huge tactical error like that.
The writers made Queen Sangria too Dangerously Genre Savvy for the heroes to easily defeat her; having her make a critical mistake is about the only way to even the playing field.
Aware that Ichigo is almost unstoppable with Budou and Ringo's backup, Queen Sangria teases them with hints that she has a way of neutralizing the other girls' powers. Ichigo then has to decide whether she should take the risk of going it alone or bring them along knowing that the queen could render her friends powerless and slaughter them.
Ichigo taunts Queen Sangria about her "cowardice", trying to provoke her into making a critical mistake like challenging her face-to-face.
Ichigo's bad decision gets her killed. Budou and Ringo are quick to follow, rendering Ichigo's main reason for choosing to go alone — protecting her friends — utterly moot.
If Queen Sangra was going to change her mind later, she's out of luck; the instant she decides to confront Ichigo alone, Lady Jaded takes her chance to seize command, making sure everyone knows exactly how bad this mistake was. Bad-guy politics are never pretty.
Reconstructed: As Queen Sangria is overpowering Ichigo, she gloats on what a Stupid Sacrifice she's making, and that her friends will be the next to die. Hearing this triggers Ichigo's Heroic Resolve, and she powers through and slays the evil queen.