The sword isn't acquired yet, its a long-term project, but I just wanted to see if the concept was acceptable.
Name: Raitankoku
What kind of weapon: Katana
What does it do: The weapon can be infused with Chakra to control lighting in a small area around it. Basically, the sword can be infused with chakra to make it glow, extending the shadows to Sîn's advantage and increasing the potent of his jutsus, or one can draw energy from the blade, which converts ambient light into very little amounts of chakra, and makes it much darker around it up to total darkness.
The sword's light emission/absorption can be changed very quickly, given that the wielder masters it well enough and has enough chakra, allowing an excellent blinding technique by flashing the light to its highest potent and then making the area pitch black.