Within many a good shonen, there are always certain types of characters, from the tomboyish female protagonist, to the battle-loving anti-hero. However, in almost every battle-centric shonen, there is what is known as a "Krillin." Named after the Dragon Ball Z character known for being bodied in almost every fight sequence, these characters serve as visual examples of an opponent's power.
A Krillin's Purpose
The actual Krillin character originates from the grandfather of all shonen: Dragon Ball Z. Krillin is something of a punching bag — a character whose main occupation is losing fights. In a world where super-powered beings scream their lungs out, grow golden hair and obliterate whole landscapes with energy beams, only the strongest can duke it out and survive. Krillin, sadly, is not one of those characters. Compared to the ever-escalating power of protagonist Goku, Krillin stands alongside fellow schmuck Yamcha as the lowest on the totem pole. As a result of his constant beat-downs, his name has often been associated with any character that is frequently defeated.
Any character that can be called a Krillin is one that deals in personal defeat. While being instantly KO'd may appear to be a Krillin's main purpose, it's actually quite the opposite, as a Krillin's defeat also reveals an opponent's power. When a Krillin is totaled, the extent of an enemy's strength is revealed, or at least understood without the hero themselves getting hurt in the process. Through the Krillin's "sacrifice," the hero can determine whether they stand a chance against this opponent, or figure out what technique will be required to come out on top.
Krillins Across Shonen
Krillins are fairly widespread across the shonen genre, with every popular series having at least one. In the classic series Yu Yu Hakusho, Krillin comes in the form of Kazuma Kuwabara, protagonist Yusuke Uramashi's best friend. It becomes clear that while Kuwabara's heart is in the right place, his only purpose in the series is to become the spiritual equivalent of a mop for villains to mop the floor with.
In Shonen Jump's Bleach, burly Yasutora 'Chad' Sado is the Krillin, constantly being overwhelmed every time he gets a moment to shine. Although, later in the series he does manage to hold his own in the few fights he's in, it's too late to redeem his Krillin-hood. Another notable Krillin is in the hit series One Punch Man, with the cyborg Genos, who sadly always gets his can kicked across the battlefield. There lies a sense of irony to Genos, as he was specially built for standing up for justice and bringing it down on those who oppose good, yet he is easily beat down with little effort.
The Tragedy (and Unintentional Comedy) of the Krillin.
Depending on the situation, a Krillin is either heavily wounded or killed outright. The frequency of this varies across each shonen series, but because it occurs at all, the existence of any Krillin has become a darkly comedic one. No matter how hard a Krillin trains, or what technique they employ, they are almost always bound to lose. It's written in stone that when a character has obtained the 'Krillin' status, they will inevitably be on the ground, defeated and thoroughly battered. They can never match up to the hero, will eventually be replaced by the hero's rival and, when the cast grows large enough, ultimately be left to languish in obscurity.
But, eventually, fate will have mercy on them, and one way or another the Krillin will finally overcome their weakness and hold their own in a fight. After witnessing them be struck down so easily countless times, the satisfaction of seeing the little guy come out on top is immeasurable. Every dog has its day and every Krillin gets a win...to hold them over for their next five losses, at least.