Ghirahim Diantia (Sword Form)

When Ghirahim was turned into a sword spirit, he took on another form, one made of a metal harder than steel. In this form, he gains a few inches of height, loses his irises to be of a solid white, and has white diamond-like designs all over his body. He has a large diamond-cut gemstone on his chest, of which was confirmed to be a hematite by a jeweler. 

In this form, his body is made of a rare metal only found in the Demon Realm: Nikotin (NIGH-co-tin). Much stronger than steel, Nikotin can take the full force of a broadsword/mace/battleaxe/etc. and not even be scratched. Its melting point is 18,368°F (10,187°C), 3x that of Tungsten, which has the highest melting point of any metal on Earth, at 6,192°F (3,422°C). Nikotin is only able to be melted by Fire Elemental demons, of whom are immune to lava and magma and can create flames up to 35,000°F (19,427°C), which is even hotter than the surface of the sun, which currently burns at 9,941°F (5,505°C). This high melting point thus makes Ghirahim able to wade in boiling lava for short periods of time, as lava burns at an average of only 2,200°F (1,250°C). He cannot do so for more than a few minutes, however, and must allow time for his metallic body to cool back down. 

He prefers his Hylian form, though, so getting to see him in this form is very rare.