Sexual, duh!

"Mmm, let's start with a fun workout. Remove your pants, please."

Ren obliged.

Sumire wasted no time mounting his cock.

"Let's see how much sexual stamina you have."

She wildly bucked back and forth, moaning as she did. She also looked at her watch, timing Ren until he came.

Ren enjoyed this 'training'. Certainly much better than the regular Phantom Thief training.