Mega Man Battle Network 4: Blue Moon is a strategic action-RPG for the Game Boy Advance, continuing the adventures of Lan Hikari and his NetNavi, MegaMan.EXE. Set five months after the WWW war, the story follows a new threat: a massive asteroid heading toward Earth. This entry introduces the 'Soul Unison' system, replacing Style Changes, allowing MegaMan to synchronize with other Navis to gain their abilities for three turns. Players must navigate competitive tournaments and battle viruses in a unique 3x6 grid combat system. The 'Blue Moon' version features exclusive Navis and Battle Chips, encouraging trading and cooperation with players of the 'Red Sun' version. With its refined combat and new 'Dark Chip' mechanic, Blue Moon offers a deep and challenging tactical experience.