Reason (理学 Rigaku) is a magical weapon skill introduced in Fire Emblem: Three Houses. Combat with these weapons involve fighting enemies using various spells. Sharpening Reason unlocks Reason Prowess.
Reason is the skill stat that governs the growth of a unit's offensive magic moveset, and as such, Reason acts as the combination of Anima magic (known in Fódlan as black magic) and dark magic. All Dark Reason magic have an idiosyncratic naming scheme where it includes a capitalized Greek letter after the name of the spell.
Similar to Fire Emblem Gaiden and its remake, every character in Three Houses has a fixed spell list that they learn & use as they improve their Reason weapon stat via tutoring or by participating in live combat as either a combatant or as an adjutant while having a black/dark spell equipped; e.g., all Byleths between players will always used the same spell list, as would other characters such as Shamir or Dorothea. Rather than having to buy tomes like in most previous titles or having an HP cost as it was in the Valentian games, every spell has a set number of usage per map. Characters replenish their spell count between maps. Certain magical classes can increase the number of usages of certain spells.
Annette has the Crest of Dominic, which allows her to occasionally conserve spell charges, allowing her to cast Reason Magic without consuming a use if it activates, which is also the case for Constance and her Crest of Noa. Lysithea and Lorenz have the Crest of Gloucester, raising the Mt of their Reason attacks when it activates, which is also the same power as the Crest of Macuil, though no one else in current history, beyond the Saint himself, has a Crest of Macuil.
List of learnable Black Magic
|Fire||3||90||0||1-2||3||E||10||Basic fire magic.||Byleth, Edelgard, Ferdinand, Caspar, Linhardt, Dedue, Mercedes, Sylvain, Lorenz, Raphael, Leonie, Rhea, Flayn, Catherine, Alois, Anna, Balthus, Constance|
|Bolganone||8||85||0||1~2||6||C||5||Advanced fire magic.||Byleth, Edelgard, Ferdinand, Caspar, Linhardt, Dedue, Mercedes, Sylvain, Raphael, Leonie, Rhea, Manuela, Seteth, Catherine, Alois, Balthus|
|Ragnarok||15||80||5||1~2||9||B||3||The highest tier of fire magic.||Byleth, Dedue, Mercedes, Sylvain, Lorenz, Leonie, Rhea, Hanneman, Catherine, Balthus|
|Thunder||4||80||5||1-2||4||E||8||Basic lightning magic.||Byleth, Dimitri, Dorothea, Ferdinand, Bernadetta, Felix, Mercedes, Hilda, Manuela, Gilbert, Jeritza, Anna|
|Thoron||9||75||10||1~3||7||C||4||Advanced thunder magic.||Dimitri, Dorothea, Ferdinand, Bernadetta, Felix, Ingrid, Hilda, Marianne, Hanneman, Gilbert, Jeritza|
|Bolting||12||65||15||3~10||18||B||2||The highest tier of lightning magic.
Cannot trigger follow-up attacks.
|Hilda, Manuela, Constance|
|Wind||2||100||10||1-2||2||E||6||Basic wind magic.||Claude, Petra, Linhardt, Ashe, Annette, Hanneman, Seteth, Flayn, Shamir, Cyril, Yuri|
|Cutting Gale||7||95||10||1-2||5||C||6||Advanced wind magic.||Claude, Linhardt, Ashe, Annette, Ignatz, Marianne, Seteth, Flayn, Cyril, Yuri|
|Excalibur||11||100||15||1~2||8||B||4||The highest tier of wind magic.
Effective against Flying foes.
|Claude, Linhardt, Annette, Seteth, Flayn, Yuri|
|Blizzard||3||70||15||1~2||4||E||10||Basic ice magic.||Bernadetta, Ingrid, Ignatz, Marianne, Shamir|
|Fimbulvetr||12||65||25||1~2||10||B||3||Advanced ice magic.||Bernadetta, Ingrid, Ignatz, Marianne, Shamir, Constance|
|Sagittae||7||90||5||1-2||6||C||10||Magic arrows with a high Hit.||Claude, Dorothea, Petra, Annette, Sylvain, Lorenz, Hanneman, Shamir, Yuri, Constance|
|Meteor||10||80||0||3~10||19||B||1||Magic that also hits targets adjacent to the point of impact.
Cannot make follow-up attacks.
|Dorothea, Hanneman, Anna|
|Agnea's Arrow||16||70||5||1~2||13||A||2||The most powerful form of black magic. A sweltering flame that reduces all to ash.||Dorothea, Lorenz, Rhea, Constance|
List of learnable Dark Magic
|Miasma Δ*||5||80||0||1~2||5||E||10||Basic dark magic.||Hubert, Lysithea, Hapi|
|Mire Β*||3||70||0||1~3||5||E||8||Basic dark magic.
Inflicts Def -5 to foe for 1 turn.
|Swarm Ζ*||4||70||0||1~2||4||E||8||Basic dark magic.
Inflicts Spd -5 to foe for 1 turn.
|Banshee Θ*||9||75||5||1~2||9||C||5||Intermediate dark magic.
Inflicts reduced Mov to foe for 1 turn.
|Luna Λ*||1||65||0||1~2||7||C||2||Intermediate dark magic.
Ignores enemy Res. Cannot make follow-up attacks.
|Death Γ*||6||70||20||1~3||8||B||4||Intermediate dark magic.
Has a high Crit rate.
|Hubert, Jeritza, Hapi|
|Dark Spikes T*||13||80||0||1~2||11||B||3||Advanced dark magic.
Effective against cavalry.
|Hades Ω*||18||65||10||1~2||16||A||2||Advanced dark magic. Calls on the morbid might of the underworld.||Edelgard, Lysithea, Hapi|
List of enemy-only Dark Magic
|Bohr Χ*||10||60||0||3~10||20||B||3||The highest tier of dark magic.
Foes hit are left with 1 HP. Cannot make follow-up attacks.
|Quake Σ*||8||50||0||All||20||B||1||The highest tier of dark magic.
Damages all units except Flying. Cannot trigger follow-up attacks.
- Constance is the only unit to learn Fimbulvetr without also learning Blizzard.
- All units that can learn Dark Magic have some connection to Those Who Slither in the Dark; Edelgard, Lysithea, and Hapi were experimented on by members of those who slither in the dark. As the Death Knight, Jeritza's faction affiliation is those who slither in the dark. In Hubert's Paralogue in the Crimson Flower route, Darkness Beneath The Earth, Hubert is called on to help mages of those who slither in the dark.