Shipping, a practice that romantically pairs characters together, is one of the oldest tenets of fandom culture, covering everything from Star Trek to Dragon Ball Z. For the past few years, the website Tumblr has been ranking the top 100 ships for its users as part of its annual Fandometrics report.
Tumblr has long been a great resource to gain insight into trends in fandom, shipping included, even as the site's popularity has decreased. In regards to anime in 2019, most of the most popular ships are what you would expect. High ranking couples included Sasuke and Sakura from Naruto, Natsu and Lucy from Fairy Tail, Victor and Yuri from Yuri on Ice!!! and almost everyone from My Hero Academia, the show that topped the site's list of the most blogged-about anime of this year.
The highest-ranked ship from the series -- and in fact, the highest-ranked anime ship of all -- isn't two of the most prevalent, Midoriya and Ochaco or Midoriya and Todoroki, but rather, its Kirishima and Bakugo, or "KiriBaku." How did this upset happen?
KIRIBAKU, EXPLAINED
Bakugo is one of the first characters introduced in My Hero Academia. He's first presented as a bully to the main protagonist, Midoriya, using his immense power to overwhelm the quirkless boy and make him feel worthless. However, after the first couple days of class, he is humbled by encounters with other students -- most notably Midoriya -- where he realizes that his powers, while incredible, don't make him all that better than everyone else.
As part of his development, he opens up to select members of his class, such as Midoriya, but more noticeably, Kirishima, who is a relatively eager and warm boy his age who teases Bakugo over how over-the-top his antics can be. He ultimately is one of the few people Bakugo trusts entirely, as seen during the Bakugo Retrieval arc where Midoriya wisely states that the only person Bakugo would allow to rescue him is Kirishima.
Bakugo noticeably becomes less hostile towards others thanks in part to his friendship with Kirishima, and it should be stated, ironically, that while Bakugo failed his Hero Licensing Exam, Kirishima not only passed but his, but is also one of the few students to gain a work study with Fat Gum's hero agency.
Despite this, Bakugo's pride drives him to work harder, and he never once takes out his anger on Kirishima for surpassing him. In fact, some of Bakugo's advice to him actually helps Kirishima survive a fierce encounter with a super-powered quirk user.
FAN CULTURE AROUND THE SHIP
On Tumblr, much of the KiriBaku fan art and posts present the two mostly in-character, with Kirishima being a supportive, loving puppy-dog and Bakugo being a grumpy, reluctant-to-say-he's-in-love-jerk with a heart of gold.
https://caffchaos.tumblr.com/post/189410997063/kiribaku
On the Hugo Award-winning fan fiction website, Archive of Our Own, Kirishima and Bakugo is the second-ranked ship in the MHA fandom (behind Bakugo and Midoriya). The majority of these stories follow a similar route, including tags such as "Bakugo is bad at feelings," and from this, we can gain a very particular sense of what appeals to fans about this ship.
Twitter contributions to the culture around the ship also feature much of this same dynamic, with Bakugo being a grump, which allows Kirishima to be as affectionate as possible.
The "grumpy boy being treated with love and affection" angle is what gives the ship a unique and specific appeal. While Bakugo verbally thrashes most other people around him -- which leads even the League of Villains to mistakenly see him as a potential candidate for recruitment -- he remains very good at heart. He's just a very naturally aggressive person. That goodness in the canon of the story is brought out by his friendship with Kirishima, who is just a warm, loving person in general.
KIRIBAKU VS. OTHER MY HERO ACADEMIA SHIPS
The surprising thing about this ship isn't that it exists, but rather that it's this huge. While Bakugo is the main rival of the series, Kirishima is a relatively tertiary character for much of the series. Yes, in the Work Study arc the anime is currently airing, Kirishima gains a far larger role of prominence. However, he was never really a major player before that. Why, then, does this ship outrank the other MHA pairings that made the cut, like Bakugo and Midoriya (18th), Todoroki and Midoriya (21st), Aizawa and Yamada (39th), Bakugo and Ochaco (69th), and Todoroki and Momo (93rd)?
Looking at Google Trends, the ship sprang to prominence in July 2018 and has remained fairly popular since then. Its peak in July 2018 coincided with the same general time frame of the Bakugo Retrieval arc, in which Midoriya points out that Kirishima remains the only person Bakugo trusts enough to rescue him when he's captured. This one line -- affirming the friends' bond -- appeared to light a fire under MHA shippers. The moment also put the rest of the series into perspective for many fans; that their friendship had all been leading up to this important moment, leading some to revisit past episodes and track their relationship through this lens.
KiriBaku spiked in popularity again when Season 4 started airing, reaching its a new peak during Kirishima's first episode as a member of Fat Gum's hero agency, in which Kirishima needed to remember an exchange between himself and Bakugo in order to push himself to the necessary limits, giving shippers brand new material to fuel their headcanon. It also helps that, with Midoriya more isolated from his friends this season, Kirishima remains the most likely candidate for shippers to grasp onto.
All in all, the obvious answer as to why people ship Bakugo and Kirishima from My Hero Academia is simply because they think the two are just adorable together.
My Hero Academia is available to watch on Crunchyroll and Funimation.