A professor, who calls himself Okita, specialized in computational fluid dynamics comes to Eden Hall on a Christmas night. He claims to follow a star up until she enters Eden Hall. He later gets into an argument with Ryuu after declining his recommendation of having a champagne, and downing a cup of Guinness beer instead. Afterwards, Ryuu offers Okita the Black Velvet, which is a mixture of both beer and champagne. He doubted Ryuu and boastfully predicts that the drink will spill out of the glass, generally basing off the idea from his years of thorough research and study of fluid mechanics. This is not the case however, as Ryuu successfully pours both the beer and champagne simultaneously, without the mixture pouring out of the cup. It is noted in this episode that Ryuu is amongst the very few bartenders in Japan who are able to mix the Black Velvet perfectly without pouring them separately. Thus, the featured drink of episode 10 is the Black Velvet.