indepth

From the character profile found in the manga: Umi is described as being not afraid to speak her mind, she sometimes comes across as a selfish person. However, she cares deeply about her friends. She uses rapiers well because she fences. Her magical element is water.

My own analysis of Umi is that she is quite outspoken when she finds things out of the ordinary. When she first visits the Fountain of Eterna it is in 2d. Umi finds this beyond crazy and decides to rename the Fountain as The Weirdo Fountain of Eterna. Just an example of one of the many crazy things Umi thinks up. She also finds Mokona to be very annoying. Umi tries at every chance to make mischief against the "marshmallow." She's quite impulsive and often runs into trouble before she even thinks about it.

While it may see that Umi does not care on the outside about anyone, she's a very loving person who shines on the inside. Whenever Fuu or Hikaru get hurt, she tries her best to help them and worries about them constantly. Whenever someone says that Umi cares about others, Umi denies it. She can actually be quite oblivious to love, even if it's staring at her in the face.

A strong warrior, Umi's skills are honed into fencing and water elements. All her attacks are quite powerful and second only to Hikaru.