Lens of Invincibility

The Lens of Invincibility (無敵鏡) are a pair of antique glasses which Cologne had brought with her from the Joketsuzoku village. Originally it was part of a series of items worn by the infant or weak Joketsuzoku to protect themselves from bandits as they were unable to do so otherwise. The lenses are held with a stick attached to the side of them, in a similar fashion to that commonly associated with. Should the lens been worn in reverse, their effect shifts to the wearer, forcing them to bow down in tears and apologize to their opponent.

Manga history
The lens was in a box of other antiques until Mousse came across them, tried them on, and was able to defeat Cologne shortly thereafter. This caused him to believe the lens gave him increased strength as opposed to their actual ability to forcing those who look upon the wearer to bow down in tears and apologize profusely to them. He then went to the Tendo Dojo to use them on Ranma Saotome and defeat him in front of Shampoo, who had also arrived to warn Ranma. The lens worked, as Ranma fell to a large spiked ball that Mousse threw, then compulsively bowed and apologized to Mousse, asking to be hit even more. The effect wore off after Shampoo kicked Mousse away.

Back at the Cat Café, Cologne revealed the purpose of the lens, and Mousse, who had been eavesdropping, was just beginning to feel ashamed of himself. However when Ranma declared that the lens was perfect for a hopeless cheater like Mousse, this provoked the latter to try and get revenge with the lens.