Eren「エレン, Eren」or real name Elyune H. Grimwald is an adventurer and a member of Cabal's Party. She is actually the daughter of the Duke of Sorcerer's Dynasty Sarion Elalude, who ran off to be an adventurer due to her selfishness and free-spirited personality.
Eren is a really loyal teammate and friend. She quickly accepted and befriended Shizu in their party, as well as befriending Shuna and Shion in Tempest.
Eren or rather Elyune hails from the Sorcery Dynasty of Sarion where she was a noble. After she studied at Royal Capital Academy, she left the country because she wanted to be an adventurer. She yearned for the freedom of an adventurer. She and her bodyguards Kaval and Gido set off.
Eren is first seen exploring Veldora's cave as part of Cabal'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 Cabal 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 Ingracia, 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 Farmas Kingdom attacked resulting in Shion's death, she revealed her true appearance as an elf of royal status from the Sorcerer's Dynasty Sarion, 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. She later decided to join Tempest, spending the remainder of her life there.