Some anime heroes would feel a lot more at home in another series. Even if a character is the star of a show, that doesn't mean they're living in the fictional world that best suits their personalities, as their skill sets and idiosyncrasies often clash violently with their material realities.
There are a ton of anime characters that belong in other anime, and in most cases, their lives would be a lot easier if they could make the switch. Mob Kageyama of Mob Psycho 100 might have a more fulfilling life if he had someone beyond his non-psychic mentor Reigen to show him the ropes. If he went to the school from My Hero Academia, he could easily get all the supernatural info he needs.
Certain characters are doing alright in their their home franchises, but have infinitely more to offer other anime. Tohru Honda learned how to deal with sad, complicated families in Fruits Basket, so it's exciting to think about how she could help the Zoldyck family in Hunter x Hunter. In the best case scenario, both the character and the foreign series benefit from the crossover.
Saitama can defeat any opponent with a single punch, so he'd be useful in pretty much any anime centered on fighting. However, his goofy personality makes him best suited to live in the world of Gintama.
The hero of One Punch Man isn't just powerful, he's also completely ridiculous, just like everyone in Gintama. He doesn't particularly care about being a hero, as long as he garners enough recognition to get paid since his extreme couponing hobby can't cover his grocery bill.
In both series, the outcomes of fights take a backseat to mundane absurdity and poking fun at anime tropes. With his affably apathetic personality, Saitama would get along just fine with the ever-lazy Gintoki Sakata.
Despite its overall quality, Yu Yu Hakusho doesn't always live up to its full potential. While all the male characters are richly complex, the female heroes leave much to be desired, as they're rarely given a moment in the spotlight.
Yukina is a powerful ice demon who cries diamonds. She's strong-willed enough to resist bursting into tears while being tortured, and her compelling logic dissuades her brother from slaughtering people. Unfortunately, she's sidelined for most of the series, oscillating between serving as a damsel in distress, and the love interest for Kazuma Kuwabara.
Yukina's talents would blossom in the world of Naruto. Between her ice powers, healing abilities, emotional maturity, and diplomacy, she'd excel at being a ninja. A natural pacifist, Yukina could become a medical ninja rather than an assailant, or use her social skills to broker peace between warring nations.
Akira Fudo is a nice boy who just wants to help others and hang with his friends. Unfortunately, he's a character in Devilman Crybaby, so he's transformed into a wretched demon, and his terrible pal Ryo often manipulates him into hurting others.
Akira would be much better off in a shonen anime that emphasizes the importance of friendship and love. While tons of series exhibit these values, One Piece is the perfect place for the whiny fiend to call home.
As the Straw Hat Pirate crew hunts for legendary treasure, things can get pretty violent, but moments of intensity are usually bookended by periods of calm stability. No matter what happens, everyone in Luffy's crew loves and cares for each other.
Akira could easily use his superhuman powers to help the Straw Hats out, and he'd be free from the misery he endures in his own series. He's meant to have a group of loyal friends, so he's not cut out to be a monster.
Benten may not be a ghoul, but she definitely eats like one. While she doesn't consume humans, she has a taste for tanuki, or sentient raccoon dogs who freely walk about the rural parts of the The Eccentric Family's version of Earth.
One particular tanuki is named Yasaburo, and Benten constantly flirts with him. Unfortunately, she also ate his father.
Most characters in Tokyo Ghoul are members of the titular species, which means they're compelled to eat people. Since Benten actively elects to devour tanuki, she'd fit in perfectly with ghouls like Tsukiyama, who consider chowing down on human flesh an art form and spectator sport.
Benten will have to make sure the ghouls don't notice she's a human, or she'll discover what it's like to be lower down on the food chain.