About me: Euphemia is Lelouch's younger sister and was told by Lelouch that she was his first love shortly before her death at his hands due to him losing control of his Geass. Prior to the series, Lelouch, Nunnally and Euphemia would play together, and watch the stars together in Pendragon. She and Nunnally argued about which of the two would marry Lelouch and attempted to make him decide on the spot, much to his discomfort. Euphemia deeply missed Lelouch and Nunnally when they were sent into exile, and when they were announced dead when the war between Britannia and Japan happened. Eventually Euphemia then began to question who Zero is when the possibility of him having a grudge against the Britannian imperial family is revealed, remembering Zero's dialogue to her implying that he also personally knew her.
The Island of the Gods also boasts strong innuendo about their relationship. When zero confronts Euphemia a second time, she asked if he is Lelouch, to which he takes off his mask and reveals that he was alive to Euphemia, which causes her to have tears of joy seeing her long-lost brother. It's revealed that she finds Lelouch's anger towards Britannia and the imperial family justified.
Despite finding Lelouch's reason to become Zero, she however wishes that they could go back to being together. When she establishes the Special Administrative Zone of Japan, Lelouch goes against it. When he confronts her at the ceremony, she reveals she is doing it for Nunnally's sake and to protect Zero. Lelouch decides to agree with the zone, but when his Geass becomes permanent (with the order to kill all the Japanese accidentally) he then realizes that he has to kill Euphemia. As Lelouch shot her, he states that she was his first love. It was one of the greatest burdens and sins on his soul and something that he was never able to forgive himself for.
