The following contains spoilers for My Hero Academia up to and including Chapter 354, "Oopsie Daisy," by Kohei Horikoshi, Caleb Cook and John Hunt, available now in English through Viz Media.
With My Hero Academia well into its final act, many fans are expecting to see at least one major character's death before the story's eventual end. Compared to other shonen series, MHA has suffered very few fan-favorite deaths; this leads many to believe a bombshell may be on the way, but it's anyone's guess who might be saying goodbye soon. Redditor u/ForeverLastingBliss made a post detailing why the next major character death might be Fumikage Tokoyami.
In the year-old post, they explained how the two major hero deaths, Midnight and Sir Nighteye, have followed a specific trend. During MHA's Shie Hassaikai arc, All Might's former sidekick Nighteye took on a protective role when he confronted Overhaul in Mirio Togata and Deku's stead. Nighteye suffered severe injuries from that battle and died shortly after.
Midnight was placed in a similar situation during the Paranormal Liberation War. Her death followed an attempt to stop Gigantomachia in his tracks by putting him to sleep using her Somnambulist Quirk. After getting knocked out of the sky by Dabi, she was cornered by several villains in her weakened state and killed soon after.
The similarity u/ForeverLastingBliss noticed was that both characters had names that included a variation of the word "Night" in their hero names. While Tokoyami's name, Tsukuyomi, isn't as clearly linked to the trend, it still has some ominous undertones. In Japanese mythology, Tsukuyomi is the god of the moon and different interpretations claim that his name is a combination of two Japanese words; "tsukiyo", meaning moonlit night, and "mi", meaning looking or watching.
Though the pattern certainly holds true, the mere etymology of Tokoyami's hero name shouldn't be enough for My Hero Academia fans to start mourning Class 1-A's resident edgelord just yet. He's consistently proven himself to be one of 1-A's strongest members. Even in his most recent fight against MHA's boogeyman, All For One, he's been able to handle himself remarkably so far. The team of Tokoyami, Jiro and Hawks have seemingly managed to defeat the Demon Lord but without unambiguous confirmation, they're not out of the woods yet.
Tokoyami is certainly still in danger given his proximity to All For One, but the deaths of some other heroes do somewhat disprove the intriguing theory. Neither X-Less nor Crust satisfied the conditions of the "Night" theory, but that didn't save them from being turned to dust at Shigaraki Tomura's hands. The current war hasn't resulted in any deaths yet, so everyone's still fair game. If Horikoshi does decide to kill someone off, they will be sorely missed.