Welf Crozzo hails from Rakia, a nation ruled by the war god Ares, where his noble family rose to prominence by forging magic swords. His hereditary skill, Crozzo Blood, granted him the power to create these potent weapons. However, witnessing his family's greed and obsession with this power bred a deep resentment within him. He came to view magic swords as corrupting tools that fostered dependency and abandoned their wielders upon shattering. Fleeing Rakia with aid from his former goddess, Phobos, he sought a new beginning. Arriving in Orario, Welf petitioned to join the Hephaestus Familia. The goddess of smithing, initially hesitant due to the Crozzo family's tarnished reputation, accepted him after hearing his vow to never create magic swords and his commitment to forging lasting, non-magical weapons. Under Hephaestus's mentorship, he honed his craft while steadfastly maintaining his refusal. His perspective shifted during a critical battle when the Hestia Familia faced the Black Goliath on the 18th Floor. Recognizing the necessity of his abilities to protect allies, he reluctantly crafted magic swords, demonstrating their strategic value. This marked the beginning of his cautious acceptance of using Crozzo Blood responsibly, though he strictly limited creation to Familia members. Welf later transferred to the Hestia Familia, becoming Bell Cranel's personal smith and a core combat member. Driven by pride in his work and a desire to surpass Hephaestus through conventional smithing, he insisted on forging all weapons and armor for Bell and Mikoto. Despite leaving her Familia, he retained deep respect and romantic feelings for Hephaestus, vowing to create a sword impressive enough to earn her affection. A pivotal moment solidified their bond when Welf saw her scarred right eye without reacting in fear or disgust, an acceptance that profoundly impacted her. His abilities center on the Crozzo Blood skill, enabling him to forge magic swords exceeding his ancestors' creations in power—capable of restraining high-level entities like the Black Goliath or adventurers such as Gareth and the Hiryute sisters. He later developed "unbreakable" magic swords (e.g., Shikou Kazuki) that channel the wielder's magic instead of breaking, though overuse risks mental exhaustion. His combat magic, Will-o-Wisp, disrupts spellcasting by triggering explosions proportional to the target's gathered magic power, making him a natural enemy of mages. He also possesses the Veritas Burn lie-detection skill and the Blacksmith development ability, enhancing his crafting. Welf evolved from a conflicted blacksmith defined by rejecting his legacy into a confident warrior and integral Hestia Familia member. He reconciled with his heritage, selectively employing magic swords for allies' protection while pursuing mastery in non-magical smithing. His tactical awareness and leadership grew significantly, notably during expeditions into the Dungeon's deeper floors. By season 4, he acted as a mentor within the Familia, fully integrating his combat prowess and crafting expertise. Trivia includes his notoriously poor naming sense for weapons (e.g., attempting to name Mikoto's sword "Shimajirou") and amateur violin skills. His attire incorporates Salamander Wool for fire resistance and Undine Cloth for water protection.