Where do I find the secret bar, and I have the items to summon the succbus but I don't know where to do that, and how do I talk to Shizu without being thrown off the stage
The succubus can be summoned from room 13 in the clubs first floor, lower right. Knock 3 times to open it, rest should be easy enough.
Shizu is an appetizer for Takano, the club owner. Get some more girls, and then enter the club from the front, a staff member will give you a signet ring so you can meet Takano. On the second floor, go up the stairs again.
Now here's where I'm stuck, I can't get laid with Takano, and I'm not sure if it's completion, or just the right combination of choices. Wish there was a hint for that.