Historia Reiss - Ymir was romantically attracted to Historia and utterly devoted to her.

Are Ymir and Historia a couple?

Perhaps the highlight from the Q&A session is about the canonically confirmed romantic relationship between Christa/Historia and Ymir, which Maxwell states that she “ONE THOUSAND PERCENT” ships. ... “It isn't the 'unicorn' that these relationships sometimes ends up being for some shows,” she said.

Who is Ymir in love with?

Ymir is a mysterious character of the anime/manga series Attack on Titan and a main character in the Clash of the Titans arc/Season 2 of the series. She is usually seen with Historia Reiss (formerly known by her fake name Christa Lenz) who is her love interest.