Dash's Lightning is a unique weapon wielded by Silver Aura in the Side story Forgotten Light. It is a katana with a built in electroshock generator. The sword's electroshock generator is initially broken when Silver Aura appears from stasis. It was named for Rainbow Dash and displays her cutie mark on the base of the blade.
A misconception is that the sword was made for Rainbow Dash, but it was actually made for Silver Aura and designed based off of Rainbow Dash. The Design was to show loyalty to his CO.