Nyan Cat is a boy. Tac Nayn is a girl. Based on the mobile game, when Tac Nayn drinks the nrg drink, she gets a bow. Now this could be wrong; Tac Nayn could be.... Jack, u can pas aan this out, right? Assuming Nyan Cat Don't get no bow, I rest my case
Nyan cat is a boy, and Tac Nayn is a girl, proven door Nyan Cat Lost in Space, a Nyan cat app, where u can play as Tac Nayn. When u get the Adrenaline power up for Tac Nayn, (Adrenaynline) their eyes go Kawaii and a roze bow appears on their head. This inspired me to make a custom called "true Nayn" which has eyelashes, a bow, and a curious expression on 'her' face.
Nyan Cat is based off of Chris Torres', (his creator), cat Marty, therefore he is male. On twitter Nyan Cat has also been referred to with he/him pronouns. Tac Nayn is a male, as confirmed in the beschrijving of his original video.