"Mega Man Network Transmission takes place a month following the events in Mega Man Battle Network and before the clash in Mega Man Battle Network 2. A month has passed since the nefarious WWW organization tried to commandeer a military satellite. Now, cyberspace is about to encounter another menace, a new virus known simply as the Zero Virus. Once again, it is up to Lan and Mega Man to defeat this latest threat, battle bosses and solve problems in the ‘virtual’ realm. Players must communicate with Lan, Mega Man and other characters to gain pertinent information to solve various predicaments that may occur.

Mega Man Network Transmission uses the popular chip system introduced in the original Battle Network role playing game. By collecting chips, players equip Mega Man with special weapons and support items that can enhance his abilities or provide a defensive advantage. One chip can upgrade his jumping abilities; another can create a protective shield that immediately inflicts damage when attacked by enemies. The new enhanced backgrounds will create multiple levels of effects that add a new exciting element to the game play as enemy’s fire shots or are eliminated."

Story from Capcom press release

"- First Mega Man game for the Nintendo GameCube
- New visual design: All the characters have a 3-D cel-shaded art style.
- Utilizes the popular chip system from Mega Man Battle Network
- Customized attacks: Select and arrange which chips are used in battle
- More than 100 different attacks and a wide array of playing styles
- New storyline: Discover what happened in between Mega Man Battle Network and Mega Man Battle Network 2"

Features from Capcom press release