Nagasone Kotetsu who gives this blade its name was a swordsmith in late early 17th century Japan. He originally was raised in the craft of an armorer through his family, but came to study the craft of making katana when he turned 50. Explanations for his turn are rooted in much obscurity and rumor; one states that after an incident of pride during a contest between a helmet he made against the swords of the Kiyomitsu school, he turned to making swords out of shame for his actions, while another states reasons for armor losing its demand into the peaceful days of the Tokugawa Shogunate and him desiring a challenge. Due to his expertise in crafting armor, his swords were made especially to also be able to cleave through it, and was famous not only for his swords, but for how often and well they were faked.
虎徹 / こてつ / コテツ [kotetsu] in Japanese.
Final Fantasy I
Stats: ATK +22, ACC +6
Equip: ?
Drop: Cerberus
Description: A small katana designed for easy use
Final Fantasy III

Stats: ATK 105, ACC 90, weight 1, Dark damage
Use: ONK, DRK, NIN
Treasure: Training Cave, Cave of Shadows, Bahamut's Lair
Type: Katana
Final Fantasy IV
Stats: ATK 45, ACC 100, SPD +2
Equip: Edge
Buy: 11,000 gil (sell: 5,500 gil)
Shop: Feymarch
Treasure: Sealed Cave B1, Sealed Cave B2
Final Fantasy V
Stats: ATK +55
Equip: Samurai
Buy: - (sell: 5,900 gil)
Treasure: Exdeath's Castle F7
Other: can be equipped with two hands
Final Fantasy VI
Stats: ATK 66
Equip: Cyan
Obtain: ?
Description: Modest katana designed for ease of use
Other: Can be used with Bushidoand Two-handed
Final Fantasy XII
Stats: ATK 50, EVA 5
Range: 1, Charge time: 29, Combo chance: 13, Knockback chance: 0
Buy: 3,800 gil (sell: 1,900 gil)
Final Fantasy Tactics
Stats: ATK 7, Parry 15% (when available)
Range: horizontal 1, vertical up 2, vertical down 3
Equip (job): Samurai, Onion Knight
Equip (character): Sword Saint
Equip (enemy): level 12
Buy: 3,000 gil (sell: 1,500 gil)
Shop: (available after Lionel Castle in ch2) Trade cities
Description: A katana whose blade is adorned with a breathtaking carving of a tiger.
Other: can be equipped on other jobs with the ability Equip Katana
Other: can be used with Dual Wield, Doublehand and Throw
Ring of Fates
Stats: ATK 130
Buy: - (sell: 1,450 gil)
Craft: Noble's Weapon scroll
Bonus 1-star: ATK Boost 1, SP Boost 1
Bonus 2-star: ATK/SP Boost 2+Samurai Lore 2, ATK/SP Boost 2+Fast Charge 2, ATK/SP Boost 2+Tribal Secrets 2
Bonus 3-star: ATK/SP Boost 3+Samurai Lore 3+Fast Charge 3, ATK/SP Boost 3+Samurai Lore 3+Tribal Secrets 3, ATK/SP Boost 3+Fast Charge 3+Tribal Secrets 3, ATK Boost 5
Airborne Brigade

R+
Type: Katana, Element: -, Growth: Normal, Cost: 16
Attack: 1,210 (lv1), 4,861 (lv80), 5,786 (lv100), 6,710 (lv120), 7,635 (lv140), 8,560 (lv160)
Defense: 1,210 (lv1), 4,861 (lv80), 5,786 (lv100), 6,710 (lv120), 7,635 (lv140), 8,560 (lv160)
Obtain: any chest that gives this rank
R
Type: Katana, Element: -, Growth: Normal, Cost: 12
Attack: 880 (lv1), ? (lv60), ? (lv75), ? (lv90), ? (lv105), 4,980 (lv120)
Defense: 890 (lv1), ? (lv60), ? (lv75), ? (lv90), ? (lv105), 5,030 (lv120)
Obtain: any chest that gives this rank
All the Bravest
Stats: ATK +2, Number: 62, From: FF4
Equip: Samurai, Ninja, Auron
Drop: Cactuar
Description: The edge of this legendary blade never wears, nor does its brilliant light wane.
Pictlogica

Stats (lv1): STR +47
Stats (lv15): STR +75
Buy: - (sell: ? gil)
Obtain: -
Alchemy: Tachi, Magicite Fragment, Green Drop
Type: Katana, Rarity: ★★★, Element: -
Record Keeper

Kotetsu (IV)
Stats: ATK +90, ACC 95 (lv1), ? (lv5), ? (lv10), ? (lv15), ? (lv20), ? (lv25), ATK +142, ACC 95 (lv30)
Max Level: lv20 (initial), lv25 (first evolve), lv30 (second evolve)
Type: Katana, Rarity: ★★★★★
Other: enables use of the Eblan Twin Blades Soul Break when equipped by Edge

Kotetsu (V)
Stats: ATK +82, ACC 95 (lv1), ? (lv5), ? (lv10), ? (lv15), ? (lv20), ? (lv25), ATK +135, ACC 95 (lv30)
Max Level: lv20 (initial), lv25 (first evolve), lv30 (second evolve)
Type: Katana, Rarity: ★★★★★
Other: enables use of the Death Claw Soul Break when equipped by Gilgamesh

Kotetsu (VI)
Stats: ATK +80, ACC 95 (lv1), ? (lv5), ? (lv10), ? (lv15), ? (lv20), ? (lv25), ATK +133, ACC 95 (lv30)
Max Level: lv20 (initial), lv25 (first evolve), lv30 (second evolve)
Type: Katana, Rarity: ★★★★★
Other: enables use of the Bushido Dragon Soul Break when equipped by Cyan
Category: Equipment