Anime doesn't always care about dishing out legal consequences for its nefarious characters. Whether it's murder, property damage, or assault, anime characters who belong in prison are constantly committing crimes for which they're never taken to task.
Far from plot holes, anime's Wild West mentality is part of what makes the medium so much fun.
If Vegeta was locked up, audiences would be robbed of Vegeta's best quotes and riveting moments of heroism. Still, even the most intense Vegeta fans have to acknowledge the fact that if he killed a lot of people and in the real world, he'd have to answer for it.
While Naruto recognizes Orochimaru as a villain, he seems less threatening than some of the franchise's more dramatic antagonists, and ends up getting away with it. In the Boruto timeline, he's allowed to operate freely so long as he occasionally helps Konoha achieve its goals.
This shouldn't be happening—Orochimaru should be in prison for life after everything he's done. He has kidnapped, brainwashed, and murdered hundreds of children in pursuit of personal immortality.
He's also committed plenty of political crimes, like launching an attack on Konoha, killing the society's leader Hiruzen, and creating a fraudulent ninja village. He should be locked up until the end of his days, but instead he's working alongside people who he once fought and tortured.
Yuno Gasai's kill count is high enough to put anyone in prison. Her primary goal is to get herself and Yukiteru through the Survival Games, which does require her to murder others, but Yuno takes it to another level. She kills people solely because she thinks they might get in the way of her relationship with Yukiteru, even if they're not a physical threat.
While she certainly isn't the only person in Future Diary who deserves her day in court, she's probably the most notorious.
Hisoka Morow loves killing people, especially strong people who are difficult to defeat. He isn't just a fan of murder – if he was content watching horror movies, he'd be all good – he takes lives on a regular basis and gets away with it.
Lethal bloodsport isn't the only reason Hisoka should be behind bars. The killer clearly cannot be rehabilitated through any other means besides imprisonment. Hisoka's sense of empathy is nonexistent, as he's solely motivated by self-serving desires and is unlikely to ever change his ways.
A lot of people think Japan's age of consent is 13. While this is technically true, most prefectures have laws regarding obscenity and corruption of minors, which makes the practical age of consent between 16-18. Because Tamotsu and Pico's sexual relationship takes place in Tokyo, where the age of consent is 18, Pico is three years too young to be having any kind of sexual relationship with a 22-year-old.
Aside from the numbers issue, Tamotsu spends a large chunk of Boku no Pico trying to pressure the 15-year-old into sex acts he's not comfortable performing. Unless there's a special legal exemption if you're a character in a hentai, Tamotsu needs to go straight to anime jail.