Eternals introduced a whole new set of characters to the Marvel Cinematic Universe, including ten main Eternals, several Celestials, monstrous beings called Deviants, and Dane Whitman a.k.a. Black Knight. On top of all the characters featured throughout the movie, Eternals introduced another main character to the MCU in the mid-credits scene--the Eternal named Eros.
Eros, also known as Starfox, is an Eternal who is the brother of Thanos. Played by actor and pop star Harry Styles, he appears to Makkari, Druig, and Thena on their ship, telling them that he can help them find the Eternals who have been taken from Earth. While doing so he reveals he has a cosmic energy ball, like the one Ajak used to communicate with the Celestials. While Marvel has yet to reveal how and when the Eternals will move forward in the MCU, it seems clear that when they do so, Eros will be alongside them.
In the comics, Eros has powers that allow him to control other people's emotions and manipulate their pleasure centres, which leads to some interesting situations. While the MCU has made a lot of changes from the comics, there are some storylines featuring Eros which could be adapted to film or television as part of the MCU.
Eros on Trial
One infamous storyline featuring Eros has him put on trial for sexual assault, accused of using his powers to seduce a happily married woman. His father, Mentor, gets Jennifer Walters, also known as She-Hulk, to defend him in court. Eros eventually gets banned from the courtroom because he uses his powers to influence the witnesses.
Meanwhile, Jennifer starts to suspect that Eros used his powers on her when they were both working with the Avengers some time ago, and, furious, beats him up. Mentor teleports Eros back to his home planet, Titan, and stages a trial there to try and clear his name. Of course, She-Hulk is brought in as the prosecuting attorney. With She-Hulk coming to Disney Plus in her own courtroom series, this storyline seems like an obvious choice for adaptation. An episode of the series could focus on Eros and this court case, perhaps with flashbacks to the time they spent together previously.
Eros Forms The Dark Guardians
After Thanos dies, Eros reads his will and learns that Thanos plans to be resurrected in the body of another. Eros is convinced that the resurrection will happen in the body of Thanos' daughter, Gamora. He founds the group the Dark Guardians, made up of Nebula, Gladiator, The Rider, and Wraith, to find Gamora and kill her before this can happen. He seeks out Gamora's former lover Nova and then the Guardians of the Galaxy in order to find her.
It is later revealed that Thanos' vessel of resurrection was never going to be Gamora--it was Eros himself. While the upcoming Guardians of the Galaxy 3 is confirmed to be the last of this line-up by the director, this does not necessarily mean the characters will disappear from the MCU. That means that a variation of this storyline could still be possible.
Eros and Captain Marvel
Eros teams up with the comic book version of Captain Marvel in order to fight some of Thanos' minions, and they become close friends. Captain Marvel even spends time on planet Titan, where he falls in love with Elysius, one of the war lieutenants there. When he dies of cancer, both Elysius and Eros are distraught, and become closer in the process. Elysius creates a son using Captain Marvel's DNA, named Genis a.k.a. "Photon," who is raised to believe Eros is his father until he gets old enough to be told the full story.
Later, when Eros works with the Avengers, he is annoyed when he meets Monica Rambeau, as he thinks she is not worthy enough to carry the title of Captain Marvel. She eventually proves herself to him, and he apologizes and accepts her. While the MCU version of Captain Marvel is very different from the comic book version, it would still make sense for Eros to form a friendship with her and/or Monica Rambeau.
Eros and Maelstrom
While working with the Avengers, who gave him the name Starfox, Eros invites Wasp to a party held by the Eternal Sersi at the Eternal city of Olympia. He tells his Earth friends the story of the founding of the planet Titan, and, fascinated, they participate in the Eternals ritual of the Uni-Mind, merging with them into a single psionic entity. A Deviant named "Maelstrom" attempts to siphon the Uni-Mind's power for himself, and Vision and Scarlet Witch help free the Eternals from merging to prevent this.
Eros incapacitates Maelstrom by using his psionic powers. The Avengers and Eros later help stop one of Maelstrom's other plots, which involves planning to halt the rotation of the Earth. This is a story that wouldn't be super difficult to adapt for the MCU, and could work for either film or television.