Round Windmill is a Swashbuckler attack skill.
The user leaps into the air and unleashes an array of attacks while spinning on mid-air. A rather long freeze time follows after use, but enemies successfully hit by the skill will also be momentarily rendered immobile for a short time. This skill is often used when the number of members in the ally party outnumbers the enemy party's; on the other hand, using this as a solo player is a doable but risky tactic.
When performing this skill, there is a short period where the user is invulnerable to attacks, and many veteran players use this short period as an emergency evasion maneuver. However, lag affects this invulnerability effect so much that it is considered taboo to use this skill for such a purpose.
When the skill is used, the path of the user and its weapon glows, creating a shape similar to the wings of a paper pinwheel.