Heroes come in ascending rarity tiers, and each tier requires shards to star-promote - the single biggest lever for a hero's actual combat effectiveness, often more impactful than raw level alone. Hero EXP levels a hero up within its current star tier; shards push it to the next tier entirely, unlocking new skill breakpoints along the way.
Prioritize your MAIN CARRY hero - whichever hero anchors your chosen troop type - well ahead of the rest of your roster. A single hero pushed to a high star tier with a completed skillset consistently outperforms three or four heroes left half-invested. Spreading hero shards evenly across your whole roster is one of the more common ways new players slow their own progress without realizing it.
Hero EXP and shards are both earned through daily tasks, events, and the Hero Trial rotation, so consistent daily play matters more than any single big push. When a season introduces a promotion path (e.g. turning a strong SSR hero into a UR), check whether you already own a viable candidate before spending elsewhere - it's often one of the most efficient power jumps available in a season.