Base Class: Barbarian
You can still enter a rage traditionally as a Barbarian does, but to use some of the features below, you require a focus known as a stim. Applying a stim is a free action, but it can only be done if the character is already in a rage, and they have at least one hand free to apply the stim. The stim must be applied to bare skin. Any features that require the stim to be active indicate as such in their description. Any features that use a stim remain active as long as the character is still in a rage. When it wears off, so too do any stim-based features.
Twitch
Years of using combat stims have made sleep a very foreign concept to you. You only require 4 hours rest to complete a long rest, and you remain aware during this rest.
Relentless
Spend a free action to activate your stims. You become unstoppable. Your movement speed increases to 50 ft. for this combat turn. You are immune to opportunity attacks during this movement. You must move in a straight line. During your move, you may make a single melee weapon attack against all monsters that are within five feet of any point along that path. If any creatures are directly on the path, then that attack is made with advantage. Additionally, those creatures must succeed on a DC 14 Strength save, or be pushed 5 feet off the path in the direction of your choosing. Creatures may not suffer two attacks from the same use of this feature.
Adrenaline Surge
Spend a free action to activate your stims. You can give yourself an unnatural boost of speed, letting the combat drugs improve your reflexes and your reaction times. You immediately increase your initiative result by an amount equal to 1d6 + your Dexterity modifier. Your new order in the initiative is effective as of the next turn.
Unwilling to Yield
If you would be reduced to 0 hit points, then at the end of your attacker's round, you can immediately take a reaction to perform a move action and then a weapon attack is out of combat order. You may take this extra move and attack even if you've already acted in this round, or if the damage you've taken would automatically kill you. At the end of this bonus round, your hit points are reduced to 0 regardless of any healing you received during your bonus round.