Creed Diskenth (Black Cat) fused with Imagine Blade Level 3.
After his final Hōgyoku transformation, Sōsuke Aizen's (Bleach) right hand fused with his Zanpakutō, Kyōka Suigetsu.
Ichigo Kurosaki (Bleach) fused with Tensa Zangetsu.
Baishin (Bleach) fused with his Zanpakutō.
After Awakening, Priscilla (Claymore) assimilated her claymore into her own body.
Dante (Devil May Cry series) merged with with his own sword, Rebellion, and his father's sword, Sparda, not only allowing him to unlock his Sin Devil Trigger...
...but manifest a new sword from his very being, Devil Sword Dante.
Nizō Okada (Gintama) fused with Benizakura.
Gintoki Sakata (Gintama) fused with Lake Toya.
Tōshū (InuYasha) fused with Dakki.
InuYasha (InuYasha) fused with Sō'unga.
Nico Minoru (Marvel Comics) is merged with the Staff of One, which emerges from her body whenever her blood is shed.
Kisame Hoshigaki (Naruto) fused with Samehada.
Wapol (One Piece) fused with an entire armory.
Saga (One Piece) fused with Shichiseiken.
Ruber (Quest for Camelot) uses a special potion to merge human beings with weapons...
...doing so with himself and Excalibur to ensure no one would ever take it from him.
After 10 years of fighting against dragons, future Ragna (Ragna Crimson) merged with his silver sword.
A samurai (Yu-Gi-Oh!) equipped with Fusion Blade Murasame Blade.
Cyber Blader (Yu-Gi-Oh!) equipped with Fusion Weapon.
Rubilax (Wakfu) like all Shushu can fuse with their Wielders.
Tatsumi (Akame ga Kill) fully bonded with the Demon Armour: Incursio.
By merging with his revolver, Vash the Stampede (Trigun) can form his Angel Arm.
After his transformation into a one-eyed ghoul, Koutarou Amon's (Tokyo Ghoul) quinque, Doujima 1/2, merged with him, becoming a kagune he could bring forth to replicate it.
Zero Kiryu (Vampire Knight) merged with his anti-vampire handgun, Bloody Rose.
Nero (Devil May Cry) merged the Yamato into his Devil Bringer, allowing him to manifest its power in his Devil Trigger.
The Longinus Canis Lykaon (SlashDog) was born from the fusion of the Divine Beast Lykaon and the Ame-no-Ohabari the most powerful divine sword of Shintoism.
as the host of the Canis Lykaon, Tobio is also symbiotically linked to the Ame no Ohabari and can also summon the sword from within himself.
Crona's (Soul Eater) Demon Weapon, Ragnarok, was melted down into Black Blood and bonded to him.