Lupin III's previous love interests make a cameo appearance in this episode: Rebecca Rossellini from Lupin III (2015) and Diana Archer from Lupin III: The Pursuit of Harimao's Treasure (1995) (the lady with the yellow submarine).
The episode reveals that, like in the second manga, Lupin's regular face is just a mask, and not even his closest friends know what he looks like, although it's hinted by his silhouette that his mask is close in appearance to his regular face. The unmasking is also to make a metaphorical point about Lupin dropping all pretense to show Fujiko how important she is to him.