Aramis is the most emblematic character of the series. At 22 years old, Aramis is a brave and kind musketeer who hides an old wound and a secret revenge.

The Three Musketeers: The year is 1625. The young D'Artagnan arrives in Paris at the tender age of 18, and almost immediately offends three musketeers, Porthos, Aramis, and Athos. Instead of dueling, the four are attacked by five of the Cardinal's guards, and the courage of the youth is made apparent during the battle. The four become fast friends and embark upon an adventure that takes them across both France and England in order to thwart the plans of the Cardinal Richelieu. Along the way, they encounter a beautiful young spy, named simply Milady, who will stop at nothing to disgrace Queen Anne of Austria before her husband, Louis XIII, and take her revenge upon the four friends. 
(Source: AniDB)

Aramis fell off her horse and received the aid of a man named Francois. They fell in love with each other at first sight and spent their time happily for a while. Francois was killed by Manson and the Ironmask`s people, so Aramis swore revenge. Then she went to Paris to be a musketeer. 
1 year after the end of TV series, D'Artagnan had a drink with 3 musketeers and found that Jussac and the Cardinal's Guards harrassed a woman in a tavern in Paris. Of couse, they fought Jussac and the Cardinal`s guards and won. On his way to home, D'Artagnan witnessed the woman whom he rescued from Jussac about to jump into the river, and rescued her again. D'Artagnan brought her to home but she disappeared soon. After a day, D'Artagnan heard that the woman was killed last night and Rochefort and Cardinal's guards arrested him for murder because his hat was found by the woman's body. Aramis discovers that the story has a link with Catherine de M&eacute;dicis, and launches out an investigation. This one will bring back her to the castle of her beloved where she will have to face Pizzaro to protect a dangerous document. 
(Source: AniDB)

Based on The Three Musketeers by Alexandre Dumas. 
Note: The pilot episode of Anime Sanjuushi.

D'Artagnan leaves his hometown of Gascogne for Paris in order to join the King's Musketeers or the Guards of the Cardinal. At his arrival, he went into an argument with Athos, Porthos and Aramis and provokes them into a duel. At the time of the duel, they were interrupted by the Guards of the Cardinal who are enforcing the King's decree banning duels. Afterwards, D'Artagnan and company became friends and adopted the motto, "all for one, and one for all". (Wikipedia)