As a shonen anime, My Hero Academia is riddled with narrative turns, some to progress the story and others just for dramatic effect. In fact, the existence of plot twists is vital to all forms of artistic expression, because it ensures that the overused Hero's Journey trope is made just a tad more refreshing.
That said, there are events in My Hero Academia that are dressed up and paraded as plot twists but come as a surprise to literally nobody—neither viewers nor the characters themselves deem these moments to be anything other than expected. Some of them are even painfully predictable.
Endeavor Turns Into A Good Father
Endeavor is an odious man when introduced during the Sports Festival arc. However, after All Might's retirement, he begins taking himself seriously, attempting to make amends with his estranged family.
The slowness of his journey combined with the lack of alternative paths makes Endeavor's transformative process rather obvious, regardless of how monumental his character's redemption actually is.
Shoto Unleashes Both Aspects Of His Quirk
Shoto's first arc is filled with thoughts of anger and resentment towards his father, to the point that he promises never to use his left (or flame) side. Deku manages to convince him to manifest it regardless, asserting that the Quirk belongs to Shoto and not Enji.
However, there's no possible scenario in which one of the strongest U.A. students will ignore half their strength forever. The only surprise is that Shoto breaks out of his funk quite early in the story.
Deku Learns About One For All's History
Deku first notices his predecessors while fighting off Shinso's Brainwashing, setting the stage for his eventual discovery of the One For All narrative.
Fans correctly speculated that he would learn more about his inherited Quirk, which happens when All Might explains how the power works. That said, the full potential of One For All is unknown to everyone; even the eight who held it before Deku have a barebones understanding.
All For One Breaks Out Of Tartarus
All Might defeats All For One in a no-holds-barred showdown in Kamino, a battle that ends with the villain thrown into the most secure prison in Japan, Tartarus.
It initially seems that he has given up on his goals in favor of his so-called successor, Tomura Shigaraki, but allowing another person to wield his precious Quirk is so out of character for All For One that it's patently suspicious from the start. As such, AFO breaking out of Tartarus is not just predictable but expected.
Uraraka Is Defeated At The Sports Festival
Bakugo informs Uraraka that he has no intention of losing the round, a warning she dismisses by running full-tilt towards him. Unfortunately, her incredible maneuvers are crushed by her opponent's Explosion Quirk, an inevitable outcome of battling him during his personal arc.
There is little anticipation as to who is going to triumph—Ochaco Uraraka's childhood ambition or Katsuki Bakugo's overwhelming need to prove that he's better than Deku.
Deku Transforms Kota's Hero-Hatred Into Admiration
One of the three focal points of the Mountain Rescue arc is Kota, a small child who loses his Pro Hero parents to a villain attack, subsequently losing faith in the concept of heroism itself.
He is rude and churlish to Classes 1-A and 1-B, refusing to accept that their academic struggles will bear any fruit. Kota's hatred is converted to admiration when Deku risks his life to defeat Muscular, a personality conversion that is seen coming from a mile away.
Lemillion Loses (And Regains) His Permeation Quirk
In his fight with Overhaul, Lemillion loses the upper hand when Shin Nemoto fires a Quirk-destroying projectile at Eri. The young hero's Permeation instantly disappears, but this doesn't stop him from keeping Eri safe.
A few manga arcs later, Lemillion apologetically requests her to Rewind his Quirk back to him, which she is more than happy to do. He might be a fan-favorite character even without Permeation, but it was always going to come back to Lemillion.
Bakugo Learns Deku's Secret Before Anyone Else
In the beginning, One For All's secret is known by exactly nine people: All Might, Deku, Principal Nezu, Sir Nighteye, Recovery Girl, Gran Torino, Naomasa Tsukauchi, Kyudai Garaki, and All For One.
The tenth person to find out is Bakugo, who is also the first to learn it from Deku, albeit by chance and some pretty nifty deductions. This revelation may seem like a plot twist, but there's no other character who could have learned it before Bakugo. Further, All Might notes that the two boys are finally starting to become friends after this point.
All Might's True Form Is Revealed To The World
Although audiences (and Deku) are shocked to discover All Might's true form, the event takes place in the second episode and doesn't count as a twist because none of the characters have been built up yet.
Nevertheless, it's only a matter of time before All Might's injuries are revealed to the general public. During his face-off with All For One, the My Hero Academia world is taken aback when their Symbol of Peace appears in a weakened state, but fans obviously aren't.
Deku Will Become The Greatest Hero
Deku goes from Quirkless to inheriting the most important Quirk in existence, One For All, and he pushes it beyond all conceivable limits through the course of the story.
In fact, he achieves even greater power in recent manga arcs, the details of which include way too many spoilers. In any case, there is no doubt that Deku will become "the world's greatest hero," as he mentions during episode narration sequences. All he needs to do is overcome MHA's final villain.