Tenjou is the incredibly wealthy student council president who also happens to be a masochist and rose knight.
Being the only child of an incredibly rich church, Tenjou is self-absorbed and will publicly humiliate anyone who gets in his way. In front of others (specifically naming girls and high ranked officials) he will be charming and as handsome he can be (like Tamaki.) Because of his charm, people don't see how utterly gross he is but other guys steer clear of him knowing perfectly well what his fancy words mean.
Although Tenjou is a charmer with words, he has very strange ideas of how one should act to friends and where the boundaries of obsession lies. As seen when people refer to him and Mutsuki as friends, he freezes for about four minutes. Where boundaries lie, he decided to take it upon himself to have an obsession for the Rose Princess and has a room dedicated in his house for every occasion they've ever met, acquainted, or hung out.
Also he makes it apparent when talking to Anis further in the series to hint at bondage to "punish" him or "treat" him with her thorns (since the Rose Princess has the ability to shoot thorn vines from her hands to threaten the knights to her bidding) instead of average ropes. At some point, the author even had to cute out his graphic descriptions.