Before the game begins proper, Hypno-tan is captured within an orb that puts her to sleep and teleports her into a dread castle on a hill. There, she learns that The Magician, the master of the castle, has plans to turn her into one of his greatest minions.
Hypno-tan by herself is powerless, in terms of offense. Like Hub-favorite Shantae, she uses her hair as her most basic form of self-defense, using her ahoge to hypnotize low-level enemies to fight off other enemies, serve as stepladders, or unlock sturdy rooms. As time goes on, she can unlock more weapons, with the capability of enslaving more types and a greater number of enemies. A pocketwatch, friendly parasites, a slave-tattoo-placing glove, hypno-beam ring, etc...
If she wishes, Hypno-tan can elect to finish off the bosses (The Magician's previous great minions) with hypnosis, rather than having her own slaves destroy them. The bosses would typically be weak to one form of hypnosis in particular, and become weaker as their health rolls down. Likewise, as willpower falls, they will become slower and take off less health/will of their own. At full health, their will is nearly indomitable (just enough to allow for a challenge/super-pacifist run :P). If they can be subdued, you may summon them at any time to assist you with power-attacks, enslaving hordes of enemies at once, or even taking chunks off boss willpower. However, they maintain the health you enslaved them at, and cannot be healed.
Each boss has unique attacks which can cause Hypno-tan to temporarily attack her own allies, eroding a bit of her willpower each time. Depending on how you swing, you can test different forms of mind control on each one, or push them to try different forms of control on you.
The Puppeteer - main attack involves minions attempting to push you into place in order for wires to secure you.
* There are several false loot-chests in his boss room, which will cause living costumes to jump out and ensnare you.
* If you are too elusive without using many attacks, a giant pocket-watch may descend from the ceiling to freeze you in place when facing it.
The Slime - main attacks involve tentacles, slime snakes and enveloping.
* If you attack the tentacles and minions, it will grow a hypnotic eyestalk that will pursue you, forcing you to automatically walk in its direction if idle. As your willpower fades, you will begin walking toward it during even slight moments of idleness, and have to hold down the opposite direction to break free.
* If you mostly attack the main body, it will split off a slime-clone of Hypno-kun, and emit pheromone-laden gas that, if inhaled, will cause you to stop and make out with the clone.
* If your minions are especially aggressive with it, it will drop crawling parasites that will force you to attack your own allies on contact.
The Siren - Attacks using musical notes that can force Hypno-tan to drop an item, walk into a trap, or temporarily remove her sweater (draining will). She can emit a sonic aura that makes backing away harder the closer Hypno-tan is.
* If Hypno-tan successfully escapes the aura a few times, the Siren will swoop in to kiss her with a move that drains HT's willpower, and refills her own.
* If you are especially aggressive, she uses her ultimate attack: a soundwave that covers the screen, save for a few hiding places, and puts all enemies to sleep until woken on contact.
The Mad Scientist - "room" type boss, who you need to fight through four brainwashing rooms in order to get to. Different paths towards the main body yield different dangers, such as robotization beams, fem/futa chemical baths, or microchip-injecting cyber-spiders. These dangers will not erode willpower by themselves, but send you walking back towards one of the brainwashing rooms in question.
The Magician - attacks using a variety of orbs which can absorb Hypno-tan or her allies, causing them to temporarily transform into various bodies/personalities.
* Utilize too many power-attacks, and he'll use full-powered eye beams on you, creating an illusory version of the entire boss room; turning it into an inescapable dungeon, or perhaps a sugar-sweet paradise, each of which saps great amounts of your will.
* Use too many minions, and he'll summon ghosts in order to possess them (with twice their original willpower), and possibly you.
Five "bad" endings will see Hypno-tan enslaved to each boss... however, depending on whether or not being submissive to any of them sounds appealing to you, you can just choose to fail whenever :P . The worst ending involves falling to basic enemies, in which case The Magician changes his mind about you, and simply makes you into a disposable minion.
EDIT: Ogodei-Khan is a mind-reader.