Rainfal Slash is a Swordsman Class skill used by Master Swordsman. It is an area skill.
Master Swordsman falls from the air and cuts a large number of people within a certain area in a single vertical slash.
The Ultimate Quest - Cobalt Caste Inflitration
Master Swordsman fell from the sky after being teleported into Cobalt Castle by Choco Bibi and used Rainfalll Slash to cut a group of Magic Soldiers.