Pokémon Heart & Soul is a complete, open-source GBA ROM hack that faithfully demakes the Johto and Kanto regions from HeartGold/SoulSilver onto the Modern Emerald decompilation. This fully playtested adventure features the classic storyline reimagined with following Pokémon, a dynamic day/night system, HGSS music, toggleable mechanics (physical/special split, Fairy type), and Generation 1-3 Pokémon plus their later evolutions. Version 1.2.1 includes built-in Nuzlocke and Randomizer challenge modes, 16 gym leader rematches, the Battle Frontier, customizable shiny rates, and extensive quality-of-life improvements like HM-free field moves and quick-catch prompts, delivering a polished, community-driven experience that honors the originals while providing modern conveniences for all playstyles.