Most of the dramatic irony found in anime is based on secrets. The audience might know the secret, but the characters are unaware. This causes tension not only between the characters but also between the show and its viewers.
However, not all secrets are best-kept. Some secrets are kept from a few characters, while everyone else is fully aware. Other secrets weren't supposed to be revealed but did so prematurely. From secrets known by a few characters, to secrets that spread like wildfire, confidential information is often leaked in anime.
10 Midoriya Possessed One For All In My Hero Academia
After seeing heroic potential in Izuku, All Might gave him the Quirk One For All. There were many reasons to keep this a secret. One for All could potentially make All Might and Midoriya targets. They also didn't want anyone at school to become angry or envious. They tried to keep their secret, but it got out. Even Bakugo finds out eventually and possessed the quirk for a short time.
9 Naruto's Dad Was The Fourth Hokage
The Third Hokage and the rest of the Hidden Leaf Village leaders decided to keep Naruto Uzumaki's parentage a secret to keep him safe. His father's identity as the Fourth Hokage was kept secret for the majority of the series.
This doesn't mean it was a secret to everyone. Older characters were constantly dropping hints to Naruto about his connection to the Fourth Hokage. The older ninja certainly knew Minato was Naruto's father. Besides this, Naruto's resemblance was striking. They were lucky Naruto was that dense.
8 Naruto Had The Nine-Tailed Fox In Him
Most of the higher-ups knew Naruto was the Jinchuriki of the Nine-Tailed Fox Spirit, but somehow the entire village knew about his connection to the Nine-Tails and ostracized Naruto. Only Naruto and the rest of the children in the village children were not privy to that information.
This secret wasn't kept from Naruto or viewers very long as it was revealed in the first episode. Not to mention the Fox's chakra had it's own physical manifestations. By that point, everyone knew, making this one of the worst-kept secrets in anime history. Still, the Akatsuki somehow had a hard time tracking Naruto down.
7 Spike Was Alive In Cowboy Bebop
Spike Spiegel was constantly being chased by the Syndicate. So, he decided to lay low as a bounty hunter. He refused to do jobs that got him intertwined with the Syndicate as a way to try and keep his existence a secret. That didn't last for long.
Despite Spike's efforts to keep his life and involvement with the Syndicate a secret, the cat got out of the bag pretty quickly. It would have been difficult to hide that from Jet and Faye for too long, anyway.
6 Yato Was Actually A Violent God In Noragami
Yato wanted to distance himself from his violent past and make a name for himself as a god. However, he certainly was not fooling anyone in the deity community. While he may have succeeded in keeping Hiyori Iki and Yukine in the dark for a little bit, it was not long before his past caught up to him.
Not only did Bishamon constantly try to hunt Yato down for what she perceived as a crime he committed against her a long time ago, but Yato's own "father" and manipulator was also out to catch him.
5 Maid-Sama's Misaki Was A Maid Cafe Employee
Misaki Ayuzawa was called the Demon President at school, but she worked at Maid Latte. She tried to keep this a secret, as it would likely ruin her hardened reputation. However, it was not long before someone found out.
The school's other top student, Takumi Usui discovered her secret and saw a golden opportunity to woo Misaki. She was forced to go along with his antics, but the two eventually became close and started dating. Her secret job was no longer a secret thanks to Takumi.
4 Ouran High School Host Club's Haruhi Was A Girl
Haruhi started working with the host club at Ouran High School, an all boys school, after breaking an expensive vase. The only problem is, Haruhi is a woman. She got roped into it when the host club's de facto leader Tamaki Suoh mistook her gender, but she ended up liking the job.
While she succeeded in keeping her gender a secret from her clients, the rest of the gang already had an idea. Tamaki took a long time to put two and two together, but he eventually did.
3 The Avatar Reappeared In Avatar: The Last Airbender
While Aang was good at escaping and used various disguises, he was not exactly inconspicuous. Not only did he accidentally activate the Avatar statues in one of the Air Temples, notifying the entire world of his return, but he also caused widespread damage and chaos everywhere he went.
Team Avatar was not necessarily trying to keep everyone from knowing the Avatar was back. They wanted to let the villages know that help was coming. However, they did need to hide from Prince Zuko and the rest of the Fire Nation. They were confused as to why Prince Zuko kept finding them, but audiences have a good idea why.
2 Light Was Using The Death Note
Light Yagami succeeded in hiding his killings for a long time. After all, who would expect that someone could cause heart attacks and other deaths using only a notebook? Yet, someone found out eventually.
Not only did characters like L suspect Light of being Kira, the nickname for the killer, but Misa, Near, and Mello also had a pretty healthy ongoing suspicion. They had a hard time figuring out how he was doing it and getting the necessary evidence to take further action.
1 Celty Was A Supernatural Being In Durarara!!
As if her coach, Shooter, was not conspicuous enough, Celty was a Dullahan that never took her helmet off because she was headless. Plenty of characters in the franchise knew about this. Izaya Orihara knew, and his entire plan centered around her.
Additionally, there was another character walking around with Celty's head on her shoulders. If Celty was trying to keep her existence a secret, as Shinra Kishitani was, she wasn't very good at it. Soon her secret became the crux of the antagonist's plans.