Although the the normal viewer may be able to tell, the characters in the show can't tell Darian from Tuxedo Mask. (Note: This little fact seems to be true of all the characters that transform) Initially Serena does not like Darian at all. He makes fun of her and calls her "Meatball-head" after her tell-tale hairdo. Darian is a quiet individual and mostly keeps to himself.
Tuxedo ,Mask shows up a lot when Sailor Moon is in trouble. He always graces the scene at the last moment when all seems lost. A rose flies across the screen and sticks in the ground and Tuxedo Mask tells Sailor Moon what to do. She developes a huge crush on Tuxedo Mask. Little does she know he's Darian in real life! Now, as for Tux, we eventually see Darian talking to himself about his history and something missing in his memeory. There we find out that his parents died when he was very young and he's been an orphan ever since.
This scene also is important in the future because he rreveals that he dosen't know what he's doing (even he doesn't realize he's Tuxedo Mask in the beginning)or who he is, but he knows in his heart that helping and protecting Sailor Moon is right. Of course later on we find out why! Eventully Sailor Moon and Tuxedo Mask are forced to reveal their ture identities to each other. After this, Darian is struck down while protecting Serena and she begins to cry. The basic outcome of this important episode is that we find out Serena is the Moon Princess of the Moon Kingdom that Luna was sent to find, and Darian is really Prince Darian of the Earth kingdom, long ago in love with the Moon Princess. In short, they were destined to be toghter.
Tuxedo Mask is a solitary kind of guy, and keeps his own agenda mostly to himself. On occasion he seems to go against the Sailor Scout's agenda, but he is always working against the Negaverse. He even does so subconsciously when he is a prisoner of Queen Beryl.