Ultimate is one of the actions that are a part of the Royalguard Style in Devil May Cry 3. When executing this action, Dante will create an all-impervious force field that cannot be broken and transfers his life force into it.
Ultimate creates a force wall in front of the player. But the shield works differently from regular Block. Whenever an enemy attacks the shell, it doesn't stagger the demon and turns taken damage into life force. The move can be held for a longer period, which makes it easy to protect yourself. However, unlike Block, it takes a more time to set up a force field, which makes the player vulnerable over that time.
When executing this move, Dante will pull one his hands back and touch his devil arm by piercing his fingers on it, and with the second he puts his hand in front of him and a tri-circular yellow field will project. When this shield is damaged, the power goes into Dante's health. However, with strong enemies, such as Bosses, their might is strong enough to be able to shatter the shield and thus damage Dante in the process.