Solar Core:

Your Solar Core has four levels of charge: Dim, Glowing, Blazing, and Overheated.

• Dim – Default state, no charge.
• Glowing – After 2 rounds in combat or taking fire or radiant damage.
• Blazing – After 4 rounds in combat or dealing fire or radiant damage in two consecutive turns.
• Overheated – After 6 rounds in combat or landing a critical hit while Blazing.

Your abilities become stronger the more charged your Solar Core is. However, reaching Overheated state comes with a risk: if you stay Overheated for more than 3 rounds, you suffer 1 level of exhaustion when combat ends.

You return to Dim state after 1 minute of inactivity or when you finish a short or long rest.

Solar Strike

At 3rd level, your attacks radiate solar power, increasing in strength as your Solar Core charges:

• Glowing: Your weapon attacks deal +1d4 radiant damage.
• Blazing: Your weapon attacks deal +1d8 radiant damage and ignore resistance to radiant damage.
• Overheated: Your melee attacks explode on impact, dealing +1d12 fire damage and forcing creatures to make a Strength saving throw (DC = 8 + proficiency bonus + Constitution modifier) or be pushed 10 feet back.

Additionally, when you hit an enemy, your weapon glows with bright light in a 20-foot radius (dim light for another 20 feet).

 

Solar Flare

At 7th level, you release a burst of stored solar energy, causing a flash that varies based on your Solar Core level. As a bonus action, you can force creatures within 10 feet to make a Constitution saving throw:

• Glowing: You heal hit points equal to your level in fighter.
• Blazing: Creatures who fail the save are blinded until the start of your next turn.
• Overheated: In addition to blindness, creatures take 3d6 radiant damage, and allies within 10 feet regain hit points equal to your Constitution modifier.

You can use this ability a number of times equal to your proficiency bonus per long rest.

Solar Overdrive

At 10th level, when reaching Overheated, you can choose to enter Solar Overdrive instead of resetting back to Dim. This state lasts for 1 minute and grants:

• You become immune to fire damage.
• Your movement speed increases by 10 feet.
• Your melee attacks deal an additional 1d6 fire damage to creatures within 5 feet of the target.
• You shed bright light in a 40-foot radius.

Once Solar Overdrive ends, your Solar Core resets to Dim, and you gain 2 level of exhaustion instead of one.

You can enter Solar Overdrive once per long rest, or by sacrificing half your current hit points to activate it again.

Radiant Ascent

At 15th level, your control over your Solar Core allows you to levitate using radiant propulsion. While Blazing or Overheated, you can fly at a speed of 30 feet.

Additionally, while flying, you can use your reaction to spend a Solar Core charge and release an explosive shockwave when you land, forcing creatures within 10 feet to make a Dexterity saving throw or take 3d10 fire damage and be knocked prone.

You can use Radiant Ascent once per long rest.

Additionally, you are now able to take energy directly from the Sun. While you stand in Sunlight, you can concentrate for 10 minutes to get Blazing, using this method you can not become Overheated and you turn dim the moment you are not in direct sunlight, lose concentration or enter a fight. 

Supernova

At 18th level, when you reach Overheated, you can unleash your Solar Core’s full power in a cataclysmic explosion. As an action, you release all stored energy, forcing creatures of your choice within 30 feet to make a Dexterity saving throw (DC = 8 + proficiency bonus + Constitution modifier):

• On a failure: The target takes 12d8 fire or radiant damage and is blinded for 1 minute.
• On a success: The target takes half damage and is not blinded.
• Allies within range gain temporary HP equal to half the damage dealt.

After using Solar Eruption, your Solar Core resets to Dim, and you suffer one levels of exhaustion.

You can use this ability once per long rest.