Bro, in the context of this list, doesn't mean characters who skateboard and play beer bong, though it doesn't exclude characters who might do those things. Rather, anime characters who are bros are the kind of guys who you'd actually want as a brother. They're fun-loving, cheerful guys who are loyal to their friends, and they encourage the people around them to be their best selves.
Some bros are like Kamina from Gurren Lagann and Reigen Arataka from Mob Psycho 100 - mentors who bring their younger mentees out of their shells and teach them about life. Others, like Eijiro Kirishima from My Hero Academia and Hairo Kineshi from The Disastrous Life of Saiki K are fountains of manly positivity who inspire the people around them.
No matter what role they play, all of these characters are true bros. Which ones are your favorites?
When most people think of anime bros, their very first thought is Kamina. That's because Kamina is truly the ultimate bro. Simon begins Gurren Lagann too scared to take risks, but Kamina's encouragement slowly helps him build up his self-confidence. Kamina is consistently positive, even in times of dire crisis, and he uses his positive energy to fire up everyone around him. That's why Simon loves him so dang much.
One of the things that makes a bro a bro is a strong sense of loyalty - which Kazuma Kuwabara consistently displays. At the start of Yu Yu Hakusho, he's told by a teacher that if he or any of his friends are caught fighting, his friend won't be allowed to continue working a job that he needs to support his family. Kuwabara takes countless hits from various people who try to start fights with him, refusing to fight back no matter what, for the sake of his friend.
He takes that same energy into the rest of the show and goes above and beyond to help his friends and allies whenever he gets the opportunity.
Not only is Bulat a canonically gay character with amazing hair, he's also a great example of an anime bro. He's a member of an assassination group called Night Raid. When Tatsumi, a newbie with little knowledge about the violent world he's entered, joins the Night Raid, Bulat takes him under his wing, serving as a brotherly figure for him. As a mentor figure, Bulat gave Tatsumi a ton of advice about mental and physical strength and kept him out of danger as much as possible.
Eijiro Kirishima is bursting with manly energy, but that's not the only reason he's an anime bro. He's also a genuinely kind and friendly person who will do anything for those he cares about. He's always happy to help his friends, whether it's inspiring them to work hard at hero training, or breaking the rules to help save them from kidnappers. For all these reasons, he's one of the most respected members of class 1-A, even if his quirk isn't necessarily the most impressive.