They're no different to me than temporary transmutation spells. The WoL has been temporarily turned into a frog, chicken, spriggan, minimized to the size of tinker bell, a fire breathing toad, ghosts, etc. They'd have long been turned into thralls hadn't the echo been a convenient shield.

If such temporary infatuation, which needn't be sexual - it could be comfort or seeing someone motherly, bothers because of your characters sexuality you could easily rationalize it as the primal taking the form of whatever your character finds appealing.

Note: The princess in Shisui you refer to also has an attack called Volcanic Flatulence. That is far more disturbing to me. Fiery levels of farts capable of upheaval and burns.