Railgun (超電磁砲レールガン Chō-Denjihō (Rērugan)?, lit. "Super Electromagnetic Cannon") is the special move unique to the strongest Electromaster, Misaka Mikoto. The principle behind the Railgun is simple: there are two parallel currents on either side of her hand, the first one going towards the palm of the hand and the second one coming back towards her body and a projectile that acts as a bridge between the two currents. For the Railgun to work, the driving current goes through the positive side, through the projectile (coin) and comes back through the negative side, using the Lorentz Force with the addition of Fleming's left-hand rule. The arcade coin acts as the projectile, which is propelled towards the target using the electromagnetic force. The third-ranked Level 5 is able to fire a metal projectile at three times the speed of sound by utilizing a great amount of electricity, supposedly somewhere in the region of 2.250.000 amperes, or about 1.000.000 volts, 1/10th of her power.

Misaka Mikoto's typical railgun has a muzzle velocity of 1030 m/s (2307.2 mph) and can be fired at a rate of 8 shots per minute. Her railgun is extremely accurate, only having a target deviation of 18.9 mm.[25][26] She primarily uses arcade coins as her projectiles for portability, limiting her normal range to 50 meters. The destructive power of her Railgun is said to be so great that it cannot be measured without using a pool as a dampener in order to avoid destroying the test equipment (and possibly the school).[27][28][26] Her range can be extended when she uses other objects (like iron sand) as the projectile instead.