The power that's Yuuki's feeling could be either:
A. Erection
B. Kuusetsu and co. messing with him in his mental world
C. A hidden bonus to Kyouka's ability where the more rewards her slave (yuuki) gets, the stronger he gets
D. All of the above.
Damn, Bell kinda kinky with it, you love to see it. Kyouka being jealous is always a welcome sight. Overall, it's great to have this gem back and onto the next one.