When discussing the strongest anime character to date, One Punch Man's Saitama is always near the top of the list. The artist ONE's One Punch Man tells the story of Saitama, a superhero at the pinnacle of his powers who can defeat any opponent with a single punch. Throughout the immensely popular anime's story, Saitama seeks to find a worthy opponent after growing bored by a lack of challenge due to his overwhelming strength within the supercontinent Earth.
One Punch Man has received critical acclaim and garnered high praise for its cutting-edge animation, humor, and slickly animated fight scenes. In particular, the series' continued jabs at the shounen anime-style landed universally with critics, who cite its unique premise of an overpowered, satirical protagonist as a highly refreshing concept. Saitama's seemingly infinite yet lackadaisical powers poke fun at other overpowered anime characters that have come to predominantly characterize the genre.
This is exactly why Saitama is the strongest anime character, with his one-punch gimmick shown to be unbeatable in any situation despite the lack of seriousness surrounding his storyline. Saitama's power level in One Punch Man essentially scales to meet the size of the threat facing him, meaning he is not only untested canonically but also inevitably one-ups any character he faces. While Saitama's famous one punch and imperviousness make him incredibly potent, it also is his ability to defy logic that translates into unbreakable plot armor and, therefore, an unbeatable character.
There are certainly other near-omnipotent anime characters throughout the shounen genre's illustrious history that should be included in this conversation. In any Dragon Ball universe, Goku is one such fighter whose most recent Ultra Instinct form allows him to beat any opponent, provided he is not prevented from using this newly acquired power. There is also Akira's Tetsuo Shima, who can create and destroy reality at will, making him undoubtedly one of the strongest characters in the anime medium to date. Child-like deity Zeno from Dragon Ball Super must also be in the equation here, given Zeno canonically destroys numerous realities for his own entertainment on a whim.
Yet One Punch Man's Saitama can simply beat all of these near-immortal opponents with his patented single punch technique. The nature of Saitama's character is intrinsically set to automatically be better than anything he faces, meaning he quite literally boasts unlimited power in any given situation. Saitama being written as an overpowered parody means that his character translates as an unbeatable force who subverts even the most god-like of characters' powers and makes them appear useless against him.
There is also the looming notion of Saitama's One Punch Man plot armor granted to him by anime creator ONE. The artist has previously stated that "Saitama is the strongest character and forever will be, there is nothing that he can’t defeat in one punch," which essentially draws a line under the strongest anime character debate. Essentially, then, the entire message of the One Punch Man anime is that Saitama is the strongest superhero there ever has been, is, or will be at any point in time. One Punch Man's narrative confirms there can never be any character stronger than him, meaning if Saitama were dropped into any other anime setting, he would inevitably be the strongest entity that exists in that canon. Other aforementioned characters like Goku and Zeno are undoubtedly powerful and at the peak of their potency, but Saitama's unlimited ability to warp any power scale in his favor, whether in One Punch Man's timeline or not, means he is unquestionably the strongest anime character there is.