Fat anime boys are easier to come by than fat anime girls, and they might be overpowered in some cases.
Fat anime boys, both overweight and obese, are not a rarity. Anime is more likely to have fat boys than girls, which allows for much more body diversity. Here, we want to discuss how those boys are portrayed, and maybe learn a thing or two along the way.
Minor spoilers are about to happen for Hunter x Hunter, Assassination Classroom, Sakamoto desu ga?, One Punch Man, Naruto, Steins;Gate, Accel World, and Porco Rosso. They are very minor, but you have been warned.
Fat Antagonists
Being fat is normally considered an issue, often of moral character, so it would not be surprising to see some fat antagonists. For example, Milluki Zoldyck from Hunter x Hunter is a bad guy and walking stereotype of a fat otaku that someone needs to be offended by. He eats a lot, does not move a lot, and is an immature computer-addicted otaku. He owns a figurine collection and a lot of manga, anime, and video games. He seems to cherish those possessions more than he loves his little brother Killua, but he is also cowardly and is unlikely to fulfill his promise of killing Killua if he touches Milluki's collection. He is a villain who is shown torturing Killua (ineffectively). He is a good example of a bad fat guy in anime.
Akira Takaoka from Assassination Classroom is also an antagonist, and he outright states that he eats a lot, which is why he is fat. However, he is a muscular fat guy, who has has training as a soldier, which is a different sort of fat from Milluki. He is a drill sergeant, so he knows how to move his body, even though it is on the larger side. He is not a good character, but he is a complex one, and he loses weight, although the reasons for that are mostly insanity.
Fat Strong Men
It is also important to mention the fat men who seem to use their weight in battle. For example, Pig God from One Punch Man is named like a joke, and he is fat and shown to enjoy eating a lot. However, he is a powerful fat man, one of the most powerful men in the One Punch Man universe! Also, based on how he loses the weight after a major fight, the fat might be making him strong. He is also a good person, generally speaking, and he is nice and caring about others.
The Akimichi Clan from Naruto is also worth mentioning as their weight and size are turned by them into an advantage, something to base a technique on. That might be a nod to sumo fighters; fat can, indeed, make one stronger.
Side Characters
That said, fat people do not have to be antagonists all the time. They can be side characters, too! For example, Yoshinobu Kubota from Sakamoto desu ga? is overweight. Sakamoto helps him in many ways.
For one, he is no longer bullied as Sakamoto's friend, who knows how to stand up for himself. But more than that, Sakamoto helps Yoshinobu Kubota to get a job at that universe's version of McDonalds, which leads to the man becoming more confident and finding his own talents. He does have a fixation on his hair, but it is a better thing to laugh at than his waistline.
Fat Important Characters or Protagonists
Finally, fat people can be the protagonists or rather important characters who are not bad. After all, in real life, most fat people are nice enough, and on that note, being an otaku is not a negative trait either!
Itaru Hashida from Steins;Gate is an example of a rather stereotyped fat guy, who is not portrayed as evil. He is an otaku who is into moe culture, and a hacker who is very much into computers. While he is not an antagonist, he does have some perversions, which he will readily admit to himself and others. He is just a little stranger than others, and if anything, it makes him stand out as a character, right?
Arita Haruyuki from Accel World is the protagonist and generally a good person who seems to have gained weight after his parents' divorce. He starts out timid, then becomes more assertive and figures out his dreams. He is just a good person who happens to be fat.
Finally, Marco Pagot, better known as Porco Rosso, is the protagonist of the Studio Ghibli anime Porco Rosso. He is cursed with being mostly a pig, and that comes with being fat. Despite that, he is quite a successful bounty hunter, who comes after air pirates. He is not a stereotype, and he is an active man who is more likely to be seen sipping wine than eating like a pig. He is also rather dashing and a gentleman. He is a good example of a cool fat character.
Conclusion
This is not an exhaustive list, but it was important to us to figure out some categories to put our examples into. There are fat antagonists, side characters, and important or main characters. There are fat characters that are strong and active despite their body shape, there are those who are strong because of their fatness, and there are those who are weak, which is fine too! Finally, there are characters that are stereotypical otakus and characters that do not touch stereotypes at all.
These categories can overlap, of course. Itaru Hashida is an important character who is a stereotype, while Porco Rosso avoids stereotypes while being the main character, for example. But in any case, it is nice to see such diversity in the bodies of male anime characters.