And yeah, I mean when she fires the attack like Shinki's opener, except more BS.
In short:
You would need ridiculous control over your character to survive it without being hit.
The best solution is to prevent the (Yumemi) Boss Attack from using it. Methods of prevention include countering by point score, or using a Level 4 Spell Attack to counter.
The auto-hit I've formulated is too conditional to be used. It requires a certain number of bullets and fireballs to appear on the screen, as well as the AI not charging an attack, as well as having certain Stage Enemies appearing at a certain moment. And with that many conditions, it's impractical to use it.
In short, it's sending a "Fireball Swarm" when the Stage Enemies cross the screen horizontally, so that the AI will use their normal shots to attempt to take out the enemies, completely ignoring (tested, they do ignore it) the Fireballs. This causes the guaranteed hit because their AI is locked into trying to detonate the Stage enemies, and does not stop this until the Stage Enemies are off the screen. From experience, it should be quite obvious what happens when you don't use a Level 1 Attack against a "Fireball Swarm".
Regardless, another (near-)guaranteed auto-hit would be Yumemi's Crosses. Particularly during Boss Attack. For some reason, the AI just cannot deal with them. The AI will more often than not run into the Crosses, or points where the Crosses are about to materialize. AI used was Match Mode's, which I think is sufficient enough.
And after I eat breakfast (which is a bit late I think), I'll start on PoDD Lunatic with Yumemi, and see what happens.
First (Match Mode) Mirror Yumemi Match lasted just under 2 minutes. Second one lasted about 4. Quite short if you ask me.