Bigger magic doesn't always mean stronger spells, these are the strongest and/or most effective magical spells used in all of Mushoku Tensei.

With speculation that Hiro Shimono, the Japanese voice actor of Dabi in My Hero Academia and Zenitsu from Demon Slayer, will potentially voice teenage Rudeus in season 2 of Mushoku Tensei, Light Novel sales for Mushoku Tensei have skyrocketed, with fans wanting to read ahead to the point of massive delays.

Throughout the Light Novels, especially in the latter half of the series, magic spells become exceptionally difficult to cast and powerful, respective to their mana cost. These are the strongest spells based not only on effect but also versatility and usability in combat.

Sonic Boom is an Intermediate Rank (Rank 2) Wind Spell that allows the caster to release a strong gust of wind in the direction of their choosing. As an intermediate spell, it has a shorter cast time than larger spells and requires a fairly small amount of mana.

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While Sonic Boom on its own is a fairly simple and generally weak spell, it has tremendous tactical use. Rudeus is constantly seen using Sonic Boom to both evade and get closer to his targets when in combat. As Rudeus is physically weaker than a great majority of monsters and enemies as a mage, this gives him an edge and movement advantage.

A Saint Ranked Magic Spell (Rank 4), Flash-Over is a fire spell that allows a wide area to be covered in flames instantly. Most magicians in the world of Mushoku Tensei neither have the mana capacity nor skill to properly produce Saint Ranked spells, as the stronger the spell, the longer and more difficult the incantation will be.

Most notably used in Book 7 of the Light Novels, Rudeus produces Flash-Over to wipe out a few dozen Luster Grizzlies all at once when on an A-Ranked monster dispatch quest. With Rudeus' level of mana and ability, it's said his Flash-Over appeared to look like a sea of fire and burned the majority of the monsters to ash.

A King Ranked Water Spell (Rank 5), Lightning is the more advanced version of the Saint Ranked Spell Cumulonimbus and was first used by Roxy Greyrat, teacher of Rudeus Greyrat and the second strongest water mage in all of Mushoku Tensei only surpassed by Rudeus himself. Its mana requirement is so high even Roxy with her fairly immense mana pool can only produce the spell once a day before becoming exhausted.

After casting the immensely difficult Cumulonimbus, the caster must then condense all of the magic power into a single small focal point and then "drop" that power to the ground, producing a massive pillar of lightning capable of destroying most enemies and structures alike. Though effective, it is difficult to use in high-paced battles and better as bombardment magic.

Stone Cannon is an Intermediate Rank spell and the more advanced version of the Beginner Rank Spell (Rank 1) Rock Bullet. Stone Cannon produces a typically fist-shaped stone that is shot at high velocity. Depending on how the spell is performed, the total power and speed of the projectile can be manipulated.

While most magicians don't bother to experiment with the spell, Rudeus specializes in diversifying the spell in almost endless combinations, from non-lethal rounds, explosive shells, high-speed rounds, superheated rounds, and many other variations, Stone Cannon makes Rudeus the equivalent of a one-man army. At its strongest, Rudeus produces a Stone Cannon strong enough to bodily destroy an immortal demon king with the power of an Imperial Rank spell (Rank 6).

While Gravity manipulation does not have an actual incantation in and of itself, the ability to magically manipulate gravity has been used by exactly two people in the series; Aleksander Raibaku and Rudeus Greyrat who used it accidentally in a moment of desperation. As a unique spell with no true elemental classification, the difficulty to execute this spell can be speculated to be at minimum King Ranked in difficulty.

The most efficient use of Gravity manipulation comes from the inherent ability of Aleksander's sword "Dragon King Sword: Kakujuto." Paired with Alek's God Level Swordsmanship, he uses gravity manipulation to constantly have the upper hand in tactical movement as well as keep him from falling or staggering. It gave him the edge and ability to fight and defeat multiple King and Emperor level opponents single-handedly.

A unique spell useable only by Rudeus Greyrat through imagination and voice-less incantations, Nuclear Explosion is a fire spell used by Rudeus imagining the largest explosion he can conceptually think of and pouring in a massive amount of magical power. It is speculated to be on the destructive level of an Imperial Rank Spell, if not God Level (Highest Rank 7).

Nuclear explosion is used by Rudeus against Dragon God Orsted in his attempt to destroy Orsted quickly and from afar. The sheer destruction of the spell was said to have burnt half of a giant forest to ash by only being cast in its vicinity. It was used in both of Rudeus' battles against Orsted becoming much stronger and refined by the second fight years later.

An Imperial Rank Water Spell (Rank 6), Absolute Zero is the enhanced version of the Advanced Water Spell Frost Nova with both spells used to freeze a wide area instantly. The major difference between the two is that Frost Nova only freezes the outer layer of an object whereas Absolute Zero freezes the object solid down to its core.

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Rudeus unknowingly uses Absolute Zero to freeze a large horde of monsters, a few dozen strong, completely in their tracks. He had attempted to use Frost Nova, but in his desperation to save Roxy, he poured more magic than was needed. He only learned of the power of his spell when Roxy was shocked at the staggering level of power the spell possessed.

Dragon Gate is a unique spell used only by Orsted in Mushoku Tensei, but due to his connection to the Dragon Race, the ability to use this spell may also extend to other members of the Dragon Race such as Armored Dragon King Perugius Dola. Its sheer power allows it to only be used sparingly throughout the story.

When summoned, a dragon ornamented gate is materialized and it is capable of absorbing and destroying large-scale bombardment magic instantaneously. When first used, Orsted was astonished that Rudeus' aggregate magical power when he used "Nuclear Explosion" overwhelmed the gate and caused it to crack. This means anything under at least King rank should be destroyed instantly.

Electric is a smaller-scale version of the King Ranked Spell Lightning and was created only through Rudeus' unique style of silent casting. As Rudeus' silent casting relies on him memorizing the flow of mana through his body when he performs a spell, Electric should only be capable of being cast by him.

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Though Electric has less destructive power than Lightning, its shorter magic build-up time and more accurate attack direction make it a far more versatile spell that reduces the chance of accidentally attacking allies. Regardless of its reduced damage, Electric has shown to be more than capable of knocking out or at minimum stunning significantly stronger foes, many of whom boast immortality.

Disturb magic was first used by Orsted to cancel many of Rudeus' magic spells the first time they encountered and fought one another. After his devastating loss, Rudeus devoted himself to learning it and it has become an indispensable tool in combating enemy magicians.

Disturb magic is to direct pure magical power toward opponents, and if the opponent's spell or built-up magic is exceeded or overpowered by the magic power poured into disturb magic, then it will be completely negated and the magician themselves may be partially sealed. Rudeus typically uses it in tandem with his large array of silent casted spells, and it does also weaken his spells as well, but he has more than enough magic to overcome the negation, as he boasts the largest magical capacity in history.

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