Weapon Refinery

Weapon Refinery is a mechanic in Fire Emblem Heroes which was introduced in version 2.0.

Overview
Weapon Refinery allows 5-Star Heroes to refine their weapons, granting their weapons bonus stats or effects. The majority of weapons are simply given the option to grant the wielder fixed additional stats. Several weapons can be evolved, for example Eliwood can upgrade his base Durandal weapon into Brave Roy's Blazing Durandal. Staff Wielders who have learned their 5-Star staff weapon can imbue their staff with Wrathful Staff and Dazzling Staff passives. Other weapons, such as Hauteclere and Siegmund gain unique skill passives.

Upgrading
Any Weapon Refinery performed requires Arena Medals which are acquired by winning Arena Battles and ranking in it each week. Upgrading common weapons like Wo Dao+, Silver Lance+, Assassin's Bow+ and Gronnowl+ requires Refining Stones while upgrading legendary weapon requires Divine Dew.

Upgraded effects
Each weapon has different upgrades with different bonuses. The upgraded icon of a weapon determines its upgraded effect:

🇨🇴
 * FEH WUp 1.png - Increased Might (non-staff)
 * FEH WUp 2.png - Increased Speed (non-staff)
 * FEH WUp 3.png - Increased Defense (non-staff)
 * FEH WUp 4.png - Increased Resistance (non-staff)
 * FEH WUp 5.png - Passive added (Brash Assault) (Sol Katti)
 * FEH WUp 6.png - Passive added (Dazzling Staff) (staff)
 * FEH WUp 8.png - Passive added (Wrathful Staff) (staff)
 * FEH WUp 7.png - Passive added (Fury) (Mystletainn)
 * FEH WUp 9.png - Passive added (?) (Siegmund)
 * FEH WUp 10.png - Passive added (?) (Fujin Yumi)
 * FEH WUp 11.png - Passive added (?) (Hauteclere, Nameless Blade)
 * FEH WUp 12.png - Passive added (?) (Deathly Dagger)
 * FEH WUp 13.png - Passive added (?) (Armorsmasher+, Slaying Spear+, Slaying Hammer+)
 * FEH WUp 14.png - Passive added (?) (Zanbato+, Horseslayer+, Poleaxe+)
 * FEH WUp 15.png - Passive added (?) (Cymbeline)
 * FEH WUp 16.png - Passive added (?) (Parthia)

🇨🇴
 * FEH WUp 17.png - Passive added (Distant Defense) (Eckesachs)
 * FEH WUp 18.png - Passive added (?) (Falchion (Archanean)
 * FEH WUp 19.png - Passive added (?) (Falchion (Ylissean)
 * FEH WUp 20.png - Passive added (?) (Falchion (Valentian)
 * FEH WUp 21.png - Passive added (Flashing Blade) (Wing Sword, Rhomphaia)
 * FEH WUp 22.png - Passive added (?) (Hinoka's Spear)
 * FEH WUp 23.png - Passive added (Life and Death) (Basilikos)
 * FEH WUp 24.png - Passive added (?) (Felicia's Plate)
 * FEH WUp 25.png - Passive added (?) (Sieglinde)
 * FEH WUp 26.png - Passive added (?) (Brynhildr)
 * FEH WUp 27.png - Passive added (?) (Wind's Brand)
 * FEH WUp 28.png - Passive added (Quick Riposte) (Binding Blade)
 * FEH WUp 29.png - Passive added (Death Blow) (Forblaze)
 * FEH WUp 30.png - Passive added (?) (Regal Blade)
 * FEH WUp 31.png - Passive added (?) (Camilla's Axe)
 * FEH WUp 32.png - Passive added (?) (Yato)
 * - Passive added (?) (Breath of Fog)
 * - Passive added (?) (Excalibur)

Upgradable weapons
🇨🇴Swords
 * Armorsmasher+
 * Mystletainn
 * Silver Sword+
 * Slaying Edge+
 * Sol Katti
 * Wo Dao+
 * Zanbato+
 * Eckesachs
 * Falchion
 * Wing Sword
 * Sieglinde
 * Binding Blade
 * Regal Blade
 * Nameless Blade
 * Yato

🇨🇴 Lances
 * Berkut's Lance+
 * Carrot Lance+
 * Deft Harpoon+
 * First Bite+
 * Ridersbane+
 * Siegmund
 * Silver Lance+
 * Slaying Lance+
 * Slaying Spear+
 * Hinoka's Spear
 * Rhomphaia

🇨🇴 Axes
 * Carrot Axe+
 * Hauteclere
 * Legion's Axe+
 * Lilith Floatie+
 * Melon Crusher+
 * Silver Axe+
 * Slaying Axe+
 * Slaying Hammer+
 * Basilikos
 * Hagoita+
 * Camilla's Axe
 * Ardent Service+

🇨🇴 Bows
 * Clarisse's Bow+
 * Cupid Arrow+
 * Fujin Yumi
 * Guard Bow+
 * Monstrous Bow+
 * Refreshing Bolt+
 * Silver Bow+
 * Slaying Bow+
 * Parthia

🇨🇴 Tomes
 * Bolganone+
 * Fenrir+
 * Keen Rauðrwolf+
 * Rauðrowl+
 * Tomato Tome+
 * Cymbeline
 * Bryhildr
 * Blárowl+
 * Blárserpent+
 * Blessed Bouquet+
 * Blue Egg+
 * Dancer&+
 * Keen Blárwolf+
 * Sealife Tome+
 * Thoron+
 * Dancer's Ring+
 * Green Egg+
 * Gronnowl+
 * Hibiscus Tome+
 * Keen Gronnwolf+
 * Rexcalibur+
 * Spectral Tome+
 * Wind's Brand
 * Forblaze
 * Aura
 * Excalibur

🇨🇴 Breaths
 * Dark Breath+
 * Flametongue+
 * Light Breath+
 * Lightning Breath+
 * Breath of Fog

🇨🇴 Daggers
 * Dancer's Fan+
 * Deathly Dagger
 * Rogue Dagger+
 * Seashell+
 * Silver Dagger+
 * Smoke Dagger+

🇨🇴 Staves
 * Absorb+
 * Candlelight+
 * Fear+
 * Gravity+
 * Pain+
 * Panic+
 * Slow+

Weapon Evolution
🇨🇴Source Weapon
 * Armorslayer+
 * Killing Edge+
 * Tyrfing
 * Durandal
 * Heavy Spear+
 * Killer Lance+
 * Hammer+
 * Killer Axe+
 * Assassin's Bow+
 * Killer Bow+
 * Rauðrwolf+
 * Blárwolf+
 * Aura
 * Gronnwolf+
 * Excalibur
 * Naga
 * Candlelight
 * Siegmund
 * Armads
 * Falchion (Ylissean)

🇨🇴

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🇨🇴 Resulting Weapon
 * Armorsmasher+
 * Slaying Edge+
 * Divine Tyrfing
 * Blazing Durandal
 * Slaying Spear+
 * Slaying Lance+
 * Slaying Hammer+
 * Slaying Axe+
 * Guard Bow+
 * Slaying Bow+
 * Keen Rauðrwolf+
 * Keen Blárwolf+
 * Dark Aura
 * Keen Gronnwolf+
 * Dark Excalibur
 * Divine Naga
 * Candlelight+
 * Flame Siegmund
 * Berserk Armads
 * Sealed Falchion

Trivia

 * A number of refinements reference aspects of their appearances in other games, or aspects of their original users:
 * Refining Fujin Yumi replaces its Pass with the ability to move through forests without movement penalty - in Fates, Fujin Yumi reduced all movement costs to 1.
 * Cymbeline's unique refinement boosts user's stats when a flier is nearby, referencing Sanaki's personal guard, the Holy Guards.
 * Eckesachs' refined effect not working on dragons references the fact that it's the only Legendary Weapon in The Binding Blade that does not deal effective damage against dragons.
 * Archanean Falchion's unique refinement increases nearby allies stats, referencing the unusually large number of support bonuses that Marth provides in both Shadow Dragon and New Mystery of the Emblem, as well as the Charm skill that he has in both Awakening and Fates.
 * Ylissean Falchion's unique refinement increses user's stats when another ally is adjacent, referencing the Pair Up mechanic.
 * Valentian Falchion's unique refinement causes Continued Attack when user is attacking, with post battle damage afterwards, which references the Double Lion combat art.
 * Hinoka's Spear's unique refinement working with only infantry and fliers references the fact that all Hoshidan royals are infantry or flying units.
 * Brynhildr's refined effect reduces damage the user takes from the first magic attack the user takes in combat, referencing the weapon's anti-magic damage reducing effect in Fates.
 * Regal Blade's unique refinement boosts user's stats when an infantry mage is nearby, referencing Lloyd's friendship with Nino.
 * Camilla's Axe effect and unique refinement works with nearby fliers and cavalry, referencing both Camilla's personal skill in Fates (Rose's Thorns) and the fact that all playable Nohrian royals are flying or cavalry units.
 * Yato's refined effect is the same stat bonus as one of Alpha Yato. Its refined effect boosts nearby ally if Corrin has support with them, referencing Corrin's personal skill in Fates (Supportive).