Elyun Grimwald/Chronology

Eren is first seen exploring Veldora's cave as part of Kaval's Party and is shown to be proficient in magic. She does not notice Rimuru, who was hiding behind a rock. She is next seen being asked by Fuze to go with her companions Gido and Kaval to investigate the areas in and around the forest, and is accompanied by Shizu. In the forest, they are being pursued by Giant Ants as Kaval had poked one with his sword prior to it and were saved by Shizu who is then later saved by Rimuru as she had missed out one of the ants.

Eren and her companions go to Rimuru's village and are offered food. When preparing to leave, Eren shows how she's developed an attachment to Shizu and was shocked to find that Shizu had lost control of Ifrit. She, Gido, and Kaval aided Rimuru in defeating Ifrit, as they would not give up on a friend and member of their party. After Shizu was absorbed by Rimuru, she was upset to find that Shizu had passed away, yet her and her party thought that Rimuru had not done any wrong, as he was just honoring her final request. Before departing, she and her party members paid their respects to Shizu through Rimuru's body, being so similar to Shizu's.

Later on, Rimuru requested that Eren and her companions aid him to the kingdom of Ingrassia, as it is a human kingdom and would not take lightly to Rimuru, being a slime. On the trip, she witnesses Rimuru's skills and is yet again amazed.

After the Kingdom of Falmuth's invasion resulted in Shion's death, she revealed her true identity as an Elf of royal status from Sorcerer's Dynasty Sarion, and suggested the ritual of the Harvest Festival to Rimuru to resurrect those killed, and revealed a story based on Milim's ascension to Demon Lord.