This post is a translation of what is detailed on the Japanese Soul Calibur site, called Soul Archive. The page for Soul Calibur VI can be found here.
The Japanese page for the game has far more details than what are available on the English language page.
They currently list the existence of four game modes. This is the ‘Libra of Souls,’ or the mission based mode of the game, built around the character creation system.
This is the English language trailer for the game mode:
Below will be the translation of the Japanese site’s section on this game mode.
This is a story that revolves around the creation of an original character, and the adventure they embark as they travel the world.
The story that focuses on the tale of the player.
The creation of the player’s original character
With race, equipments parts, and fighting style, the player can create their own character. It is possible to always change these throughout the course of the game!
Movement on the world map.
You may freely move around the map to search for missions, but enemies may unexpected obstruct your movements!
When you successfully complete a mission, you will gain experience. Your original character will grow stronger as you complete missions over and over. Additionally, your character gains levels, their stamina increases, allowing them to use more types of equipment.
Enjoy battles that are bound to special rules.
The missions you take on in MISSION:Libra of Soul will have you fight battles with special rules to complete them.
The way the story unfolds with these missions will even reflect if the protagonist is either too weak for the battle or overpowers it!