[quote=StarInaBox]
Dandanken, what exactly is a "blade" modification?
[/quote]

You know in ArcV they introduced a new type of duel disk. "Blade" is part where you play your monsters. Usually it goes boomerang-like. Blade modification just change shape of it.
Standard blade:
[img=http://img3.wikia.nocookie.net/__cb20140517234020/yugioh/images/thumb/8/88/Ishijima%27s_Duel_Disk.png/200px-Ishijima%27s_Duel_Disk.png]
Example of custom blade:
[img=http://img3.wikia.nocookie.net/__cb20140629183958/yugioh/images/thumb/0/01/Reiji%27s_Duel_Disk.png/200px-Reiji%27s_Duel_Disk.png]