It's been rather quiet after Lan and Mega Man defeated the WWW in Mega Man Battle Network 3. Little do they know that they're about to embark on yet another adventure. An asteroid has been spotted in outer space which is heading towards Earth, and scientists are planning to destroy it with a giant laser. In addition to this, a mysterious Navi called ShadeMan is terrorizing the Internet, sucking the life out of other Navis, much like a vampire. Can Lan and Mega Man stop this new threat?Mega Man Battle Network 4 is an RPG-like game, and a continuation of the Battle Network series. You play as two characters - a young boy, Lan, in the real world, and a Net Navi called Mega Man on the Internet. Lan can talk to people and interact with the real world, however, when he 'jacks in' to the Internet, Mega Man takes over. In addition to interacting with Navis on the net, Mega Man also encounters random viruses and battles them in a mix of turn-based and real-time battle.A new feature of Battle Network 4 is the "Soul Unison" feature - as players progress through the game, they can defeat certain Navis and earn the ability to merge with them to become more powerful. The catch with this is that the Soul Unison only lasts for three turns, and that a particular Battle Chip is required to perform it.The Soul Unisons that you acquire through the game are specific to each version - to get them all, you must link up with a copy of Mega Man Battle Network 4: Blue Moon. You can also trade different Battle Chips (some are exclusive to particular versions) and Net Battle with a friend.