Protagonists are the three main characters in the game. These characters consist of the Marine, Noir Lime, and Proxy, with the Marine being the main hero. The game is centered around these characters; they are the only means of correcting the events that went wrong in the Plazma Burst series. Nearly every level in the campaign revolves around the goals of one of the 3 protagonists, whether it be defeating all of the enemies, escaping a place of danger, or finding the Time Machine.
Allied protagonists are helpful in-game. They will assist the player in combat. The player can switch among the main protagonists at will, or when the current hero is killed. This can only be done in special cooperative levels, typically found near the end of the campaign. The allies also have different weapon sets that can help in different situations, providing vital support in the later levels.
The Marine is the main protagonist in the Plazma Burst series. He is a soldier who came from the future to stop the alien threat. He also came to stop humanity from becoming enslaved, or even becoming extinct from the Usurpation threat. Not much is known about him, other than that he is a skilled soldier. He is also friends of Noir Lime and in the second game, Proxy. He is more of a hyper-lethal vector than just a normal marine. The Marine is silent most of the time, only having brief conversations with his fellow teammates after the levels where the player plays as Proxy. He has 500 HP under the Lite Battlesuit (130 on Impossible difficulty) and 750 HP under the Heavy one (150 on Impossible). His signature weapon is Assault Rifle C-01r.
In the campaign, there are a series of levels where the player gets a chance to play from her perspective, until she meets up with the Marine. Unlike any other Protagonist, you can take off her helmet.
Proxy is a loud and talkative character, rarely keeping to herself. In the campaign she is seen frequently talking about the situation with Noir Lime and the Marine, and will shout out a few different things in battle, like "Help!" or "Over here!" or "Nice one!".
Proxy's health is same as Marine's in Lite Battlesuit - 500 on Easy, Normal and Hard, and 130 on Impossible.
The last main protagonist in the game. Noir Lime was one of the two people sent from the future in Plazma Burst: Forward to the Past, while the other one was the Marine. They were sent from the future to change the course of history in order to restore humans' freedom from slavery. Noir Lime was incapacitated by Sword Bot at the end of the first Plazma Burst game, and was carried to a Falkonian Ship. However he refused, allowing the Marine to take the ship back to Earth, in an attempt to find the Time Machine there.
It's not known what exactly happened to Noir Lime at that planet after the Marine took the ship. It's assumed that Noir Lime found (or was given) another ship, and travelled back to Earth to meet his old partner, but his ship crashed on Earth and Noir Lime died. Luckily, he was revived by the Marine and Proxy.