Earth is on high alert as an asteroid hurtles towards it, threatening destruction. Meanwhile, a mysterious figure known as ShadeMan is wreaking havoc on the Internet, draining the life force from other Navis.
As Lan and Mega Man from the previous battle join forces once more, they must face this new threat head-on. The duo will take turns between their real-world adventures with Lan and their online exploits as Mega Man, battling random viruses and interacting with a variety of Net Navi characters.
Mega Man Battle Network 4 Blue Moon is an RPG-like game that builds upon the successful formula established by its predecessors. Key to the gameplay is the "Soul Unison" feature, which allows players to merge with defeated Navis to gain temporary boosts in power. This twist requires strategic planning, as Soul Unisons only last for three turns and specific Battle Chips are needed to perform them.