Euphoria's relationship with Allen has changed majorly over the course of the series.Upon meeting Euphoria, Allen was attracted to her kind, curious, and hard-working attitude. Euphoria, on the other hand, was attracted to Allen's "foreignness", which included his appetite. After a short while, Euphoria told Allen about her past and how she had come to be an Exorcist, revealing that their stories were highly similar. They began to be paired together on missions as Allen began to speak with Komui about Euphoria getting out into the world more because of her lack of interaction with the rest of the world.
It didn't take long for the Noah Family to see the relationship developing between them and the powerful Innocence that Euphoria possessed. In order to "hit two birds with one stone", Noah Tyki Mikk and his servant, Riruka Akimoto kidnapped Euphoria in order to destroy her Innocence and to coax Allen into their lair. Allen, distraught, was unsure what to do. However, remembering Euphoria urged him into action and he quickly took up a demand with Komui to search for Euphoria.
Lavi is responsible for Euphoria's nickname "Euphie" which she is most commonly known by. Lavi and Euphoria appear to be close friends and possibly have a brother-sister relationship. Lavi tends to be slightly overprotective over Euphoria, something she notes is because she went on her earliest missions with Lavi.