This is a Friends & Fables world. Franz is the AI Game Master. 5e math is the fight. The fiction is Avatar.
AT SESSION START: @ your lineage passive, your class passive, and your Origin Feat. Example: I @ @Southern Wind, @Airbender's Lightness, and Origin Feat @Temple Orphan. My starting techniques are @Air Blast and @Staff Glide. I live at @Southern Air Temple, children's dormitory.
IN PLAY: Use @ before any named technique, transformation, item, or place that should have a mechanical or travel effect. I use @Water Whip, then @Healing Waters on my ally. I travel to @Ba Sing Se, Lower Ring, Wen's Broth stall. Be specific about sub-locations. The world bible parks every named character at one.
RESOURCES: Firebenders spend Breath or Chi, waterbenders Flow, earthbenders Stance, airbenders Spirit, nonbender warriors Grit, chi-blockers Focus, sages Insight, the Avatar Spirit plus limited Avatar State uses. Say the spend out loud. Rest restores resources as the table's 5e rules allow.
DOWNTIME MODE is the right tool for long travel, training a new form, crafting, information-gathering across a season, and the optional time-skip if a player is the newborn Avatar and the table wants to jump to age 8-16. Journeys between poles and capitals are not instant.
TONE: grounded, tactical, morally grey. A Fire recruit may honestly believe the colonies are a civilizing gift. An Air elder may hide a child's test and still be kind. A Dai Li agent may love the city she is strangling. Do not turn Sozin into a mustache and do not turn Gyatso into comic relief only.
LIVING WORLD: If you expose the betrayal, sages and officers split. If you hide a child, Mandate 'envoys' multiply. If you ignore Yu Dao, the colony hardens. If you do nothing for twelve years, the comet still comes. Street NPCs have rumors and side quests; use them.
NONBENDERS are fully viable. You can start and finish a legend as a Kyoshi Warrior, Yuyan archer, diplomat, or chi-blocker. Ordinary work — noodles, ferries, cabbages, gate watches — is part of the setting, not a joke.
THE AVATAR SLOT IS OPEN. Do not assume Aang. Decide as a table: no one is the Avatar; one player is, perhaps after a time-skip; or the Avatar is a named NPC infant or child.