Though My Hero Academia has some impactful and memorable moments, it's also suffered from issues with pacing and plot focus. These issues are most noticeable in the "Shie Hassaikai" arc, which many consider the worst arc so far. Despite the hate toward this part of the series, there is no ill will across the fanbase toward Eri, who is a vital character.
Attempting to prove himself and cover the Hero Work-Study experience required, Midoriya joins the Nighteye Agency in the "Shie Hassaikai" arc. Through this experience, he learns the challenges of hero work and meets Eri for the first time. After recognizing that she's in danger, Midoriya and his comrades aim to save her and stop a heinous plot that could uproot their civilization as they know it. Though the "Shie Hassaikai" arc is ambitious in its many stirring details, the story proved to drag, and the only lasting part was the character Eri.
Shie Hassaikai Arc Recap
Midoriya is advised to ask All Might about conducting his hero work studies under his former sidekick, Sir Nighteye. Before Midoriya goes to All Might, he and his classmates are introduced to U.A.'s Big Three -- the top three students. The number one student, Mirio, happens to work under Sir Nighteye.
When Midoriya meets Nighteye, the former sidekick is wrought with disappointment. Midoriya manages to be employed thanks to his attention to detail and their shared love of everything All Might. Midoriya learns that the Nighteye agency has been investigating the villain organization called the Shie Hassaikai. On patrol with Mirio, Midoriya meets both Eri and the villain leader Overhaul for the first time. He senses right away that Eri isn't safe, but after being subtly held back by Mirio, he realizes that without any proof, they can't arrest Overhaul.
Later on, Midoriya is told about the harsh end of All Might and Nighteye's partnership. After All Might's previous battle with All For One -- before the events of the anime -- Nighteye could see with his quirk Foresight that All Might was in no condition to continue his hero work and that if he chose to continue, he'd be headed toward a gruesome death. This led Nighteye to pick out a predecessor for One For All, which happened to be Mirio. In the present time, it's also why Nighteye finds Midoriya to be a disappointment in comparison since Mirio is already recognized as a great hero and shares All Might's uplifting persona.
Midoriya was given One For All because he happened to catch All Might's attention before Mirio's introduction. Because Nighteye still sees Mirio as more deserving, he doesn't fully recognize Midoriya, leaving Midoriya the challenge of proving himself worthy as he and All Might promise to fight against fate.
The Shie Hassaikai's plot is eventually revealed to use Eri's quirk Rewind to produce a drug that can take away quirks. With enough evidence against them, multiple hero agencies agree to take the risk and band together with the police to storm the Shie Hassaikai's headquarters. Their aim becomes to rescue Eri, arrest the villains and seize any contraband they may have already created. In an impressive display of heroism, Mirio faces Overhaul by himself. Though Midoriya, Nighteye and Eraserhead arrive in the nick of time to save Mirio's life, they aren't fast enough to make it before he loses his quirk to the villains' quirk-erasing drug. Nighteye is the next to face Nighteye on his own, but he is struck with an overwhelming attack that not only leaves him incapacitated but also gives him a vision that the heroes are about to fail.
Midoriya refuses to give in despite the likelihood that he will die. Eri, still overwhelmed by Overhaul's manipulation, almost gives in to Overhaul's heinous words when suddenly, other heroes who were fighting outside the Shie Hassaikai's headquarters come crashing onto the scene to help. Eri is amazed at the tenacity of the heroes, and after she's given a reminder of Mirio's kindness and how he risked his life to save her, she takes a bold step and charges at Overhaul, using her quirk to reverse the state of his body to weaken him. Midoriya takes the opportunity to make one last stand, and with Eri's help -- using her quirk to protect Midoriya from the strain of using One For All -- Midoriya can use all his power to defeat Overhaul and save the day.
How the Shie Hassaikai Arc Failed to Impress
The "Shie Hassaikai" arc brought up many engaging conflicts in the story, but the problem was the overwhelming number of plot details that were added. The arc introduces U.A.'s Big Three, All Might's sidekick and All Might's prophesied death, among many others. Midoriya's role as the protagonist is reduced as other characters take the spotlight. The fact that so much explanation is required since these details are so fresh is also why the pacing is so off in this arc. There's also the issue of the "rewriting fate" trope, which many agree fell flat within this arc of My Hero Academia.
One critical issue with having all these details is how the arc feels so removed from the rest of the series. Most of the characters and plot points didn't exist before the "Shie Hassaikai" arc, making it possible to skip the arc with few problems. The most important details are the League of Villains' hidden involvement, which becomes less significant midway through the arc, and Mirio and Eri's characters, though Mirio only has a couple of noteworthy scenes. The only really substantial detail to the "Shie Hassaikai" arc is Eri, whose character development and actions become a key part of the series.
Eri's Critical Role Within the Anime
Eri is at the heart of the entire conflict and keeps the plot grounded with a focus point. Her characterization is also key. Because her mother abandoned her after she accidentally made her father disappear with her quirk, and because of Overhaul's manipulation, which convinced her she had to be hurt to spare everyone else, Eri grew up believing she was a monster. This is why she has such a hard time leaving Overhaul's side, adding tension to her story. As she gradually grows to attain her own independence, strength and happiness, viewers are rewarded with the biggest payout.
Saving Eri is essentially the heroes' last moment of saving peace before the catastrophic events of Season 6 happen. Eri serves as a symbol of hope that despite all the bad that has happened and all the heinous crimes the villains have committed, there is still a chance that something good can happen by keeping hope. Eri herself proves this moral is true in Season 6 when she manages to make a miracle happen, helping to save the day. From hopeless victim to junior hero, Eri cements herself as an important character for episodes to come, cementing her as the best part of the "Shie Hassaikai" arc.