Saitama is the not-so-famous One-Punch Man, although his ability to finish battles with a single strike lead him to deplore his overpowered condition. As a result, he shows little excitement when taking on villains, reacting to his opponents' bombastic declarations in his classic deadpan.

RELATED: Saitama & 8 Other Anime Characters Who Are Always Bored

However, there have been a few occasions during which Saitama turns serious (or whatever passes for the emotion in his understanding), often altering the atmosphere with his terrifying aura. This obviously doesn't mean that anyone has the capacity to defeat, injure, or even scratch him, but seeing Saitama's serious expression is an experience in itself.

10 His First Battle With Crablante

Crablante — one punch man

Saitama isn't born with superpowers; he earns them after years of diligent, incessant training. In his youth as an ordinary man, he comes across a lobster-type monster called Crablante on the prowl for a specific victim—a young boy with an enormous cleft chin.

Saitama tries to ignore the situation but somehow ends up protecting the child, to his own surprise. He proceeds to tackle Crablante and pluck his entire digestive system through the monster's eye-hole.

9 Saitama Doesn't Take Garou Lightly

Saitama vs Garou in One Punch Man

Garou eventually reaches his pinnacle after defeating Golden Sperm in a magnificent fight, proudly revealing his personal combat style, "Monster Calamity God Slayer Fist." Despite securing a victory over S-Class heroes like Zombieman, Garou is shocked to discover that Saitama can effortlessly counter every one of the former's moves.

Over the course of their battle, Saitama attempts to lecture Garou for choosing the wrong method to his madness, all the while knocking the villain/antihero around with his Serious Headbutt and Table Flip.

8 He Uses A "Lava Squirt Gun" To Overwhelm Orochi's Gaia Cannon

Manga One-Punch Man Saitama Destroys Orochi

Orochi's most impressive ability is absorbing and emitting energy, and producing beams capable of putting Tatsumaki on the defensive. When fighting Saitama, Orochi extracts more power from the core of the planet and generates a gigantic blast of energy, but it has no effect whatsoever.

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The villain's so-called Gaia Cannon is overwhelmed by Saitama's Serious Squirt Gun, a technique that allows him to shoot lava through his hands with incredible force.

7 His Physical Performance During The Hero Certification Exam

One-Punch Man Anime Saitama Depressed Over Hero Association C Ranking

Saitama and Genos both take part in the 6th Official Superhero Certification Exam, starting with a series of fitness tests. He claims a perfect score on all of them, presumably setting unbreakable records in the 1500-meter run, side-jumping, shot-put, punching strength, weightlifting, vertical jumping, and several others.

Saitama's seriousness unfortunately does not extend to the written part of the exam, explaining why he only obtains a measly score of 71/100 (and a C-Class ranking).

6 When He Battles The Deep Sea King

Deep Sea King

Saitama has some transport trouble during the Deep Sea King's invasion, which is why he reaches the scene rather late. After saving Mumen Rider, he takes on the monster with a solemn face, displaying his practical invulnerability in the process.

As the Deep Sea King lunges at him, Saitama strikes with such power and precision that it carves a hole in the villain's torso (simultaneously annihilating the collection of ominous rainclouds in the sky).

5 Saitama's Practice Session With Genos

Saitama vs Genos in One-Punch Man

Genos persuades Saitama into testing their respective strengths on each other, taking their match to an open landscape devoid of people. The Demon Cyborg's attacks—each stronger than the previous ones—miserably fail, prompting Genos to remind his sensei about their deal: that both of them are supposed to go all out.

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Saitama acknowledges his disciple's verve by unleashing a fatal attack, the air-blast which bores through a massive mountain like it's made of paper. He obviously doesn't land the punch, lest Genos be turned into scrap metal.

4 When He Shows Sonic His Serious Side-Hops

One-Punch Man — Saitama Serious Side Hops

Speed-o'-Sound Sonic's never-ending saga of vengeance against Saitama keeps cropping up in the story, although the villain is flabbergasted by his opponent's limitless power on every single occasion.

In one case, Saitama uses his Maji Hanpukuyokotobi, or Serious Side-Hops technique, knocking Sonic out with nothing more than pure force. This feat is all the more impressive because Sonic is also capable of a similar technique, albeit greatly reduced in potency.

3 His Entire Battle With Boros

Saitama, also known as One-Punch Man, walking away after defeating Boros

While he triumphs over Boros with "strength to spare," Saitama employs his Serious Series for the first time against the alien overlord. This is because Boros survives (and rapidly recovers from) Saitama's Consecutive Normal Punches, an attack that has never failed before this battle.

His Serious Punch, on the other hand, rips through the Collapsing Star Roaring Cannon energy attack and disintegrates Boros' body.

2 Saitama Obliterates The Elder Centipede

saitama punches the elder centipede

Genos, Silver Fang, and Bomb team up to tackle the latest threat, the colossal subterranean monster known as Elder Centipede. It's clear that the three of them combined make for an incredible show of power, but it's still not enough to permanently put an end to the creature.

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King then baits Elder Centipede into a trap, drawing the monster towards him, only to have Saitama deliver a Serious Punch, seemingly out of nowhere. Elder Centipede is instantly and thoroughly shattered.

1 When He Realizes That He's Late For The Supermarket Sale

Carnage Kabuto vs Saitama

Saitama's emotional overreactions form the bulk of his character's comedic value, especially because they tend to revolve around the most mundane things imaginable. When he battles Carnage Kabuto, he is seemingly overpowered by the monster, much to Genos' shock.

Saitama's expression appears rather serious, implying that he might be in trouble for the first time, at least until he realizes that "today is bargain day at the supermarket!" and pummels Carnage Kabuto into oblivion.

NEXT: One-Punch Man: 5 Times Mumen Rider Was The Real Hero (& 5 He Let Us Down)