Mega Man Battle Network 4

Mega Man Battle Network 4, known as Rockman EXE 4​ (ロックマンエグゼ4) in Japan, is the fourth game of the Mega Man Battle Network series, released for Game Boy Advance in 2003 with two different versions: Red Sun (Tournament Red Sun in Japan) and Blue Moon ( Tournament Blue Moon in Japan ). In this game, Lan Hikari and MegaMan partake in a series of NetBattle tournaments. A sequel, Mega Man Battle Network 5, was released in the following year.

Story elements from Battle Network 4 were loosely adapted for MegaMan NT Warrior Axess and Rockman.EXE Stream.

Story
Depending on the version of the game, different opponents and scenarios will occur, as well as Double Souls obtained. In between tournaments, a criminal organization called Nebula will attack and spread corruption with the use of Dark Chips. These are Battle Chips infused with the power of darkness. They grant immense firepower compared to a regular chip, but spawns a dark soul and does a small amount of permanent HP damage to the NetNavi that uses it.

Meanwhile, an asteroid was traveling through space, heading for Earth. The scientists at NAXA (ANSA in Japan) attempt to divert it. When their laser strategy failed, they decided to send a NetNavi into the asteroid's cyberworld and change its course. The Navi was chosen through an international tournament, which Lan and MegaMan ended up winning.

Nebula attacked again, but MegaMan was able to delete the head Navi and reached the main program operating the asteroid. The program was called Duo and was planning to destroy Earth because of the high levels of dark energy. Lan and MegaMan proved through battle that all people had the ability to conquer their inner darkness, and successfully averted destruction.

Continuity
Starting with Mega Man Battle Network 4, each separate version of the Battle Network games have slightly deviating canons from one another through the game’s different supporting characters. Red Sun and Blue Moon have loose canon to the Mega Man Battle Network 5 games Team ProtoMan and Team Colonel as well as the Mega Man Battle Network 6 games Cybeast Gregar and Cybeast Falzer  versions respectively, with Higsby, Shuko, and Dingo being recurring characters in Blue Moon, Team Colonel, and Cybeast Falzar, and Raika and Mr. Match being recurring characters in Red Sun, Team ProtoMan, and Cybeast Gregar.

Battle Changes
One great difference here is the introduction of the Emotion Window. Previously, finishing off enemies with a Counter hit with anything, inclusive of the Buster, will yield Bug Frags used to trade for items. Now, the player can only counter with non-dimming chips, and doing so will grant them Full Synchro, a powerful state where the next chip used inflicts double damage. In addition to Full Synchro, there are also Anxious, Angry, and Dark Soul states.

Another thing to note is the removal of the Add Button, and the loss of two Custom slots. This has reduced the potential chip-choosing capacity, but has given way to a few things. First, the Soul Unison Button takes the place of the Add Button after MegaMan receives his first Soul. In certain souls, the missing two Custom Slots will be filled with other things, like the Shuffle button in Search Soul, and recycled chips in Junk Soul.

The player can now find Mystery Data in battles. Even a single hit from a Buster shot will destroy the data, but if the player keeps it intact up to the end of battle, they will gain bonus data, which can range from rare chips to Bug Frags.

Battle Chips
The game also introduces Dark Chips. When MegaMan enters the "Anxious" state, he cannot use Soul Unisons, but instead can use the Dark Chips, which appear two at a time in the formerly missing chip slots. These introduce several harmful effects, but at the same time grant MegaMan immense power and access to special chips that are only usable in Dark Soul.

Navi chip versions have been traded out from v1/v2/v3 to v1/SP/DS. SP chips are only obtainable by S-ranking Navis without using Dark Chips, and can be powered up depending on how fast you delete the Navi, with the attack maxing out when the Navi is deleted in under 10 seconds. DS chips are obtained only by fighting Navis under the effects of Dark Soul, or through special mystery data that appears in Black Earth.

Double Souls
Style Changes are gone; replacing them are Soul Unisons and Dark Soul. Soul Unisons are unique, version-exclusive transformations that last a limited time, require a chip sacrifice, but give MegaMan special abilities, like charging certain chips for double damage - an ability that was absent with Styles. This added more uniqueness with the transformations MegaMan undergoes.

The Navi Customizer also has a mild change. Instead of different Styles being able to equip certain colored parts, MegaMan can equip any colored part, as long as he does not equip more than four colors in the Navicust.

Other
An odd change in this game is the lack of storyline - instead, the player must play through the game at least three times to fully collect all of the items, while facing stronger versions of the viruses and bosses. Blue and purple mystery data also change what items they give if they were collected on a previous playthroughs. Most of the data collected in previous playthroughs are carried over to other playthroughs. The repetitive gameplay has been a major turn-off for most players, resulting in the bad reception the game received.

One may also notice that this game has a different art style compared to the previous ones, along with a different town layout for ACDC. These changes would later carry over into the final two games of the series.

Bosses

 * ShadeMan.EXE
 * GutsMan.EXE/AquaMan.EXE
 * SparkMan.EXE
 * TopMan.EXE
 * FireMan.EXE/NumberMan.EXE
 * BurnerMan.EXE
 * VideoMan.EXE
 * WindMan.EXE/MetalMan.EXE
 * Roll.EXE/WoodMan.EXE
 * KendoMan.EXE
 * ColdMan.EXE
 * ThunderMan.EXE/JunkMan.EXE
 * SearchMan.EXE/ProtoMan.EXE
 * LaserMan.EXE
 * Dark MegaMan.EXE
 * Duo.EXE

Secret Boss:
 * Bass.EXE

Trivia

 * The game is riddled with grammar and spelling errors, ranging from "viruses busting",  and "What a polite young man she was!".
 * In Japan, the two versions were also released together in a Rockman.EXE 4 Dual Pack (ロックマン エグゼ4　ダブルパック).
 * The names of the cars used by ProtoMan and MegaMan in the Navi car race from Rockman.EXE Stream episode 7 are RedSun and BlueMoon, respectively.
 * This game is referenced by the operators during the Drama Audio Track "Diary Alouette's Good Day" as 'Rojo Sol' and 'Azul Luna' as they were trying to pick good names for the Baby Elves.
 * When this game was rereleased on the Wii U's Virtual Console, the Trade/Multiplayer exclusive chips could be accessed instantly by checking the Chip Library.