Hi, that also happen to me, i search and the solution is go to the second trial with at last 270-300 of Arousal Max Capacity. With that you can "endure" the test. (Also i pick the tits option than rise your arousal to 265).
The other options also works, but rise the arousal over 265, i just remember xd.
Mmm thats weird, to unlock the double door you need to fight the boss Aiko (if i remember correctly) and pull a lever in the Blue door area, and then fight Feng in the red door area and also pull a lever.
I miss the part of pulling the lever in my firts game and then make me around the zone to much time xD. (Sorry for the bad english).
SPOILER FOR THE SLAVE PERK:
The foxgirl (Kotone?) also have a check list of progress (first-second will trial, aiko hard mode(don't remember 100% this) and final area boss hard mode, all of this tasks with the slave perk). This is not required to advance in the principal mission, buy give a juicy reward.
The lever is at the end of the blue trial after you beat Aiko, where you are offered to pull all three.
Do not do that, only pull two levers randomly and then go back to the previous room.
Another lever as at the end after you beat Feng, the Minoraut girl will offer to pull it with you and you have to accept. The fact that you can only see a red button means this is already completed, so you have to finish the blue trials first.
