Born as the Third Princess of the Britannian Imperial Family, Euphemia is portrayed in Code Geass as the half-sister of the series' protagonist and antihero, Lelouch Lamperouge.

In addition to the Code Geass anime, Euphemia is featured in subsequent media adaptations of the series, including OVAs, manga and a musical in which she is played by male actor Shun Mikami.

Euphemia li Britannia appears in the Code Geass anime series, being voiced by Omi Minami in the original Japanese dub,[4] and by Michelle Ruff in the English version.

[11] After finding Zero while stranded on a mysterious nearby island called Kamine, Euphemia, having deduced Lelouch's identity from their earlier encounter, convinces him to unmask, promising to keep his alter ego a secret.

[7] Returning to the mainland, wanting to help Zero and instill trust in him for the civilian populace, Euphemia announces on live television her intent to form the Special Administrative Zone of Japan in the region under Mount Fuji, giving the Japanese people their name and country back, and govern it alongside Zero.

[20] Euphemia is featured in the manga adaptation of Code Geass, whose plotline presents some changes in the character's story that differentiate it from the one seen in the anime, such as the fact that she attended Ashford Academy for three days before becoming the Viceroy of Area 11, which consequently leads her to discover that Lelouch and Nunnally are alive.

[21] Euphemia also plays a major role in the manga Code Geass: Nightmare of Nunnally, succeeding with the creation of the Special Administrative Zone and gaining the support of the Six Houses of Kyoto.

[24] Shun Mikami played Euphemia in an all-male musical entitled Code Geass: Lelouch of the Rebellion -A Prelude Dedicated to the Sorceror-, which took place in Tokyo from June to July 2012.

[25] Euphemia's popularity has made her a frequent subject of cosplay, causing a trend in which female fans of Code Geass attempt to replicate her iconic look.

[30] Devin Nealy of Comic Book Resources (CBR) stated that of all the characters to best Lelouch intellectually, Euphemia is the only one to combat his rigid logic with idealism.

Isler also complimented Michelle Ruff's voice acting as Euphemia, saying the actress "does a great job of portraying her child-like innocence, even as she's compelled to commit murder.