The Victory Bonus increases your score for winning Battles, allowing you to complete Stages faster and progress through each Area of Super Spell Heroes.
After winning a Battle, your Hero’s Skill Rank is multiplied by the Victory Bonus to calculate the final score. Each time the Victory Bonus is used in this way, it is reduced in relation to the final score; the more the score is boosted, the more the Victory Bonus is reduced.
However, you can increase your Victory Bonus by winning Battles and increasing your Heroes’ Skill Ranks. Each time a Hero achieves a new, highest Skill Rank, the Victory Bonus is increased by a corresponding amount; the higher the new Skill Rank, the greater the boost to the Victory Bonus!
Be sure to regularly switch between your Heroes to keep achieving new Skill Ranks and increase your Victory Bonus!