[Request] Flonne's weak spots

Flonne was captured and taken to a mysterious isolated location, although Etna ultimately found her, she saw the angel bound to a device, completely vulnerable with her arms stretched up, and decided to tickle her armpit for fun. Upon this discovery that Flonne is very ticklish, she grins and doubles down on it, looks like it's gonna take a while for Flonne to be freed from the contraption.