Digimon Adventure 02 Tag Tamers

Digimon Adventure 02: Tag Tamers is a game released in 2000 for the Bandai Wonder Swan, based on the Digimon franchise. It is the second in a WonderSwan series, the sequel to Digimon Adventure Anode Cathode Tamer and continues the story of Ryo Akiyama.

Shortly after watching the defeat of Diablomon, Ryo and Ken Ichijouji are visited by a V-mon, who takes them into the Digital World to confront another Diablomon which was loose in the Digital World... which was only a ruse by Millenniumon to draw Ryo back into the Digital World, and he splits the Digital World in half, separating Ken and Ryo. Ken meets his own partner, Wormmon, and he and Ryo are forced to work separately to reconnect, meet again, and confront Millenniumon together.

The game goes in a different direction from its predecessor gameplay-wise, instead playing as a more traditional Role Playing Game, a trend that would continue for the rest of Ryo's series. It also implemented evolution of Digimon and encouraged the use of Jogress evolution to build up strong partners. The game was followed up by Digimon Adventure 02 D-1 Tamers, which gets to the important part: exactly how the hell Ryo, ostensibly a Digimon Adventure character, ended up in the Digimon Tamers Alternate Universe anyway.

Tropes present in Digimon Adventure 02 Tag Tamers:

 * All There in the Manual: Part two of Ryo's really long, unexported manual. Even worse, it also acts as a partial manual for Ken's backstory and the events which turned him into the Digimon Kaiser, and the final scene where Ken gets a Dark Seed after defeating Milleniumon is even shown several times in Adventure 02.
 * Continuity Snarl: This game offers a couple of inconsistencies to events depicted in Our War Game and Adventure 02. While Ken did travel with Ryo and Wormmon during his first time in the Digital World as seen in the anime, he entered it alone from his own house and returned from it in the same place; while it is possible that Ken did visit the Digital World once before the events of this game and Our War Game, one would assume that he would've first met Wormmon during his first trip (ie the events of Tag Tamers), though a flashback does show Wormmon with both Ken and Ryo.
 * If Ken did experience Our War Game and go into the Digital World after that, he should be more aware that it's not just a game, and that it has significant real world consequences. While he was proud and smart, he would also notice the nukes being sent off or the computer viruses, both of which were attributed to Diablomon.
 * On a much less significant note, Ryo's cameo in Our War Game showed him watching the Diablomon fight from a mountain in a foreign country, accompanied by someone who definitely isn't Ken.
 * Degraded Boss: In the game's opening, Diablomon is, well, exactly as threatening as it was in Our War Game. Then the game actually starts, and V-mon can defeat the first boss Diablomon without needing to evolve at all.
 * Rocks Fall, Entire Digital World Splits
 * No Export for You
 * Off-Model: It's almost like they had no idea what Diablomon actually looks like.
 * Start of Darkness: The epilogue, set a year later, shows Ken first realising his Digimon Kaiser persona.
 * Tag Team: As its name suggests, the game is a variation on this: Ryo and Ken are separated, and the player switches between playing them at various intervals and can use Reload Machines to swap items between each other as the game necessitates.