Ronie Arabel is Kirito's valet who learns swordsmanship under him.

She is the daughter of a 6th class Noble Family; like Tiese, she entered Sword Mastery Academy trying to raise her family status.

She was one of the top 12 of her year, so she became a valet, but what she does not know is that Kirito did not choose her. Instead she was left along with Tiese after all other elite swordsmen selected their valets. The reason for this was that they were from the lowest Noble Class, so none of the noble elite swordsmen wanted to take them as their valets.

(Source: Sword Art Online Wikia)