Being a hero is all about perspective, like in My Hero Academia, which announced a new season this year. Being a hero can be an occupation and you can even be a hero for a single person.
In the case of most anime, being a hero is about doing the right thing despite your weaknesses, and the fact that a character does this alone can also make them a hero. Anyone can be a hero in anime, and a hero isn't always strong, but not everyone has what it takes. Thankfully, the shonen subgenre provides some great examples of heroic characters who also have weaknesses, for every fan to learn from.
Yamcha (Dragon Ball)
Once regarded as Dragon Ball, Yamcha has fallen far from grace. Compared to the rest of the humans on Earth, Yamcha's strength is inhuman. An ode to this was the fact that he was one of the few who stood on the front lines when the Saiyans first appeared to take over Earth.
But as the series progressed, his strength stagnated significantly. He died to mobs during the invasion, so nowadays, he doesn't stand a chance against the galactic threats. Though he vanished into obscurity, it shouldn't be forgotten that he has the ability to fly and the ability to shoot energy balls from his hands.
Shigekiyo Yangu (Jojo's Bizarre Adventure: Diamond Is Unbreakable)
While not possessing any of the scariest stand abilities in Jojo's Bizarre Adventure, Shigekiyo Yangu was a side character who, for the majority of the series, stood out as a nuisance. Both his ability to manipulate an army of miniature stands and his obsessive greed to the point where he tries to kill his only friends made many fans detest his existence.
However, all that changed when he heroically spent his last few moments uncovering the identity of Yoshikage Kira for his friends to see. At that moment he displayed an impressive level of craftiness and intelligence when using his stand to fool the genius killer and it was strong enough to contend against Josuke and Okuyasu.
Tenten (Naruto)
Tenten stands as one of the most unfortunate characters in shonen history and she was simply a forgotten character in the Naruto series. Initially, a lot of importance was placed upon her as a member of what was considered the strongest Genin team. As a trained ninja, she is incredibly skilled in combat. However, her specialty is using throw-able weapons.
Being a throwable weapon expert in a world where most enemies are capable of using a jutsu that can shield them even if they were standing in the middle of nowhere is not exactly a good sign of her strength. However, she proves to have a lot of potential, as seen when she invents her own jutsus to fit her style, despite coming from a civilian background -- a feat not many Jonin-level ninjas can do.
Ciel Phantomhive (Black Butler)
Ciel Phantomhive's position as the main character is that of a master, with his main strength being his servant, Sebastian Michaelis the Demon. Despite being a 13-year-old boy, he almost never acts his age. He displays a level of shrewdness and intellect that even makes adults decades older than him nervous.
Despite the magical themes the show presents, Ciel himself is relatively weak. As stated, his main strength is his servant in conjunction with his intellect. He takes a commander position and his servant does all the actual heavy lifting. This is not exactly anything for him to be ashamed of though, as most people after his life possess an inhuman level of strength and ability.
Mr. Satan (Dragon Ball)
In the world of Dragon Ball, a slightly above-average human like Mr. Satan is the least likely hero to appear in a universe full of beings who can destroy planets with waves of their hands. With his background as a skilled martial artist, he can take care of non-threatening issues like thugs or gangs. Compared to the average human, he displays a superhuman-like level of strength and speed.
The funny thing about Mr. Satan, though, is his refusal to believe that beings like the infamous Cell and Majin Buu are out of his league. In the end, he sees himself as a protector of the innocent, as seen when he challenges Cell before any of the Z-Fighters. Despite going up against beings that could kill him with a flick of their wrist, Mr. Satan can be relied upon to show up.
Usopp (One Piece)
Usopp is another character in the Shonen genre whose strength does not derive from his physical prowess. But he isn't exactly super intelligent either. Instead, he is something more of an inventor or mechanic who makes his own weaponry that he uses against his opponents. For that reason, he is known as the "Sniper King," thanks to his remarkable marksmanship in tandem with his inventions.
Once known as a coward, Usopp stands as one of the One Piece world, where almost every strong opponent possesses a technique to move quickly, his accuracy is often tested. He's a character who, compared to his compatriots, is the weakest when dealing with more than one opponent.
Minoru Mineta (My Hero Academia)
Minoru Mineta is a character who fans have complicated feelings about when it comes to My Hero Academia, as his personality doesn't exactly fit someone who desires to be a hero. To put it frankly, he's a pervert who gets on the nerves of both boys and girls. His martial prowess is nothing impressive either, in fact, he may be the weakest in the entirety of Class 1-A.
But despite being one of the most hated characters of My Hero Academia, Mineta is still someone that can be considered a hero. His ability allows him to pluck sticky orbs from his head that only lose their stickiness when he wants them to, making this a useful ability for restraining opponents. The orbs are bright and easy to dodge, but limited in quantity when Mineta can only remove a certain amount from his head before bleeding.
Hiyori Iki (Noragami)
Before becoming a half-spirit, Hiyori Iki was just a normal high-school girl who knew nothing of the supernatural events occurring in her world. But thanks to her half-spirit form, she was granted several abilities: enhanced speed, strength, and senses. But even with these powers, she mostly stands on the sidelines during the series' conflicts, and for a good reason too.
When in her spirit form, she has a tail which ends up being a major weakness that enemies could exploit. Her major strength relies on being there for the main characters, and it's because of her that many internal conflicts are solved. It is also because of her that Yato, the forgotten god, doesn't fade away. Thanks to her ability to read memories, she has become a valuable member.
Tsukune Aono (Rosario + Vampire)
While it's uncertain whether Rosario + Vampire can be considered an old anime that stands the test of time, it was incredibly popular in the early 2010s. But compared to its manga counterpart, the protagonist of the anime, Tsukune Aono, is significantly weaker and just an ordinary high school boy before he mistakenly enrolled in a school for monsters.
As such, he's constantly surrounded by entities that can unintentionally kill him. If he didn't happen to become friends with some stronger monsters at the school, then that might have been his exact fate. But despite all that, he doesn't show a hint of fear as he interacts with these inhuman entities. In the end, as far as the anime is concerned, Tsukune is just an average human in a world of monsters who sometimes succeeds with the aid of mystical tools or monsters.
Mumen Rider (One Punch Man)
Mumen Rider is, without a doubt, the most heroic person in all of shonen anime. Despite being a normal human, he races onto the streets with his trusty bicycle battling monsters and villainous people all for the sake of saving others. Even when faced with insurmountable enemies, he never hesitates to put his life on the line if it means giving others hope, as seen during the Deep Sea King incident.
Despite being the #1 C-Class Hero, Mumen Rider is by no means the strongest C-Class Hero. His rank comes more as a sign of approval by the populace who see him as a greater hero than those with inhuman strength. He is neither skilled in martial arts nor incredibly intelligent, he's just a normal guy who can get back up, no matter the setback.