Soul Parade is a pretty powerful and unique defensive technique used by Brook, one of the members of the Straw Hat Pirates from the anime series One Piece. This technique is directly connected with Brook's devil fruit, Yomi Yomi no Mi, and his primary sword, Soul Solid.
The Yomi Yomi no Mi allowed Brook to come back from the dead and become a living skeleton, with special powers associated with his soul. It is the weapon known as Soul Solid, whereby Brook imbued the dark power of his soul into the cane sword, allowing it to create tremendously cold temperatures when the blade is in contact.
Soul Parade is the technique of Brook, or otherwise known as "Souru Parādo", and is one of his strongest defense techniques. In this move, he backhands Soul Solid to block any attack thrown at him. The ability to make anything he blocks this way freeze acts as both a defensive wall and a counterattack. The freezing is a direct result of Brook being able to channel the icy power of his soul right through his weapon.
Soul Parade comes in handy during his battles against more powerful enemies, which includes the arc of PunkHazard when Brook made use of his Soul Solid to counterattack some strong enemies that touched either of their different parts of weapons or their Limbs that he was able to trap them in an ice limit for a while, long enough for him to turn the tables.
For Soul Parade to be successful, the importance of Brook's Soul Solid and the power of Yomi Yomi no Mi come in handy. His special abilities allow him to add a level of versatility in his fighting style that very few other characters can. This is paramount with respect to Brook's place both as a swordsman and, of course, among the musicians and Straw Hat Pirates.
In the anime, this is shown in a pretty cool way: each time this technique is performed, there is always a graphic, visible change in the ambient temperature, often with frost or ice fast forming upon contact with the Soul Solid. It shows the chilling power Brook can keep and gives it an aesthetic value to the fights.
More significant than simply being used in combat, the Soul Parade has a thematic relevance in itself because of its connection to the soul and the world of the afterlife, elements of which Brook also very strongly represents. A character who has literally come back from the dead, Brook's techniques often highlight his ethereal nature and the supernatural abilities of the Yomi Yomi no Mi. This is topped off by Brook's epithet, the "Soul King," under which he performs as a musician, fusing his combat prestidigitation with the artistic persona.
Another strong point of Brook's usage of Soul Parade is in the context of his character development. They probably think of him as an airy, almost comic character, and the character development of Brook through many episodes has had a few critical points to help display that serious determination and mental/come intellectual brawn in battle. Techniques such as Soul Parade are indicators of his development, bringing out his capability of using his unique skills creatively and efficiently.
Popularity of Soul Parade has revived with the increase of fans, to the point that the creators integrate it into most One Piece merchandise and fan-made works. Copies of Soul Solid, Brook's cane-sword, are put to sale so that fans can feel related to him as regards his nature of fighting. Social media websites also come out with a variety of video and fan arts that focus on Brook's techniques, also Soul Parade, to show these particular fans that he and his combat skills have sunk into their minds.