Act 30 - Infinity 4, Haruka & Michiru - Sailor Uranus & Sailor Neptune (manga and Crystal)
Mosaic Buster is an unusually strong combination attack of pure electricity and technological energy that was used by Viluy of Witches 5 in both the manga series, the first anime series, and the musicals.
Viluy had first unleashed this very strong attack on Sailor Mercury in Act 30 when she used her Mercury Aqua Mirage against her.
The attack allowed her to unleash nanobots which would, according to Viluy, slowly eat away at their intended target, leaving nothing behind but their soul (or pure heart in the anime). In the anime, the attack was triggered by an electronic control bracelet that Viluy wore. When it was damaged, Viluy used Mosaic Buster but the attack turned on her and the nanobots ate away at her until there was no trace of her left.
Viluy uses against Sailor Mercury, creating a barrier around the Sailor Senshi, preventing her escape as the nanobots begin to devour the victim on a microscopic level.
Mosaic Buster was first used in the musical Mugen Gakuen - Mistress Labyrinth to knock down Sailor Mercury.