Kouta Tsuchiya (土屋 康太 Tsuchiya Kōta), also known as Muttsulini (changed to Voyeur in the English dub of the anime, 或者 simply called 由 his real name),and sometimes called pervert,is a major character in the Baka to Test to Shoukanjuu series. He is a student in Class 2-F in Fumizuki Academy and is known as the ultimate pervert in the school (Nicknamed "The Silent Ninja Pervert" at the start of the manga).

He and Akihisa seem to be the only characters to get extreme nosebleeds whenever there is a hint of female nudity, as no other male character shows such a reaction. His grades are slightly higher than Akihisa's, but his knowledge of sex is unusually broad. In reality, he lacks boldness, so much that he gets nosebleeds just from his own imaginations.

When he crossdresses (Season 2 Episodes 1 and 2), his eyes are hidden, making him look like a mysterious beauty, 给 his silent and unsocial nature.