WONDERSWAN - Digimon Adventure 02: Tag Tamers
Release date: August 2000
Digimon Adventure 02: Tag Tamers is the second game in the series of four featuring Ryo as the main character. He's joined in this game by young Ken Ichijouji from Digimon season 02. The second season aired from April 2000 to March 2001 and Tag Tamers gave Ken (and Digimon Kaiser) a backstory.
STORY SYNOPSIS:
Ryo's visiting Ken when he's once again summoned to the DigiWorld to help Gennai, Tai and the Digimon fight Diablomon. It turns out that Diablomon is just a front from Millenniummon to lure Ryo back. Ryo and Ken must now fight Millenniummon's evil Digimon, collect the digimentals to evolve their Digimon and face Millenniummon himself in the end. They however have to fight separately because Millenniummon's evil powers split the DigiWorld into two mirrored sites and they're both caught in one of them. Their only way of communication is through Gennai's Reload Machine that enables them to send items and Digimon to one another.

Gameplay is a bit different here than in Anode/Cathode where you have a battle grid and must first move towards the opponents to be close enough to fight them. Tag Tamers has repeating 3 on 3 battle arenas but (at least I think) the evil Digimon have more special attacks/skills with different effects on the player's Digimon - some are poisonous and can paralise (like Floramon), Clockmon can turn back time to the beginning of the battle - basically resetting it - and some can jinx you with a defeat after your third turn is up. I really liked these although they frustrated me a lot. I found the switching between Ryo and Ken and clearing the same dungeons and servers twice a bit exhausting but I can see the appeal if someone is really invested in evolving their Digimon.
The quotes are taken from Yesterday's amazing script translations. I've only changed the names of the Digimon because ugh I'll just forever stick to the dubbed ones.
It's summer of 2000 and Ryo is visiting Ken, who called him over because there's a strange creature popping up on his computer screen. When he shows it to Ryo, he realizes the creature had changed.
The creature on the screen is Diablomon and he's suddenly joined by WarGreymon and MetalGarurumon. They fight, Diablomon defeats the two Digimon and Ryo seems to have a panic attack, he starts spinning around scaring Ken.
They're actually witnessing the fight against Diablomon from the second Digimon movie Our War Game.* They decide to send the Digimon an email of support and although the emails sent to Izzy's computer in the movie slow WarGreymon and MetalGarurumon down, the two Digimon manage to fuse to Omnimon/Omegamon and defeat Diablomon. Tai thanks everyone for their help: "Omegamon was born with the power of everyone's mail!"
(* we do see Ryo in the actual movie but he's not with Ken at his house, he's somewhere in the mountains connected to the internet on his laptop)
Another Digimon appears on Ken's computer the next day and Ryo comes back again. D-3 digivice flashes on the screen and this time it's Veemon. He asks for Ryo's help and both Ryo and Ken join him in the DigiWorld. They're greeted by Agumon ("Ryo! We met again, right?"), Gennai and Piccolomon. Veemon urges Gennai to explain the situation.
They decide to go to Gennai's house and Wormmon leads the way. They get into the town, that is suspiciously empty and find Gennai unconcious with Tai and Agumon still frozen. They wake him up and explain about the explosion. Gennai comes to the conclusion that they are now in a mirror world.
So Ken and Wormmon go and fight the evil Digimon with the help of two more Digimon (for me that were Patamon and Salamon), getting closer to Millenniummon with each their win. At one point Ken returns to Gennai's house where he's introduced the Reload machine, that can turn the worlds of the two mirror sites back into one. This only works for a moment and can be used to exchange items and Digimon between Ken and Ryo. Gennai uses it to send a letter explaining the situation to Piccolomon and Ryo. They now know they both, Ken and Ryo, have to clear the dungeons of the evil Digimon on both mirror sites. Every time they clear a dungeon Millenniumon's power is down by one.
This is when you walk around the DigiWorld, open new portals to new continents of the world, clear the dungeons of the evil Digimon, use the reload machine and do the same in the mirrored world. This is the part I spent way too many hours on because I'm so lame at games that I didn't even try to make it easier for me (the game being in japanese wasn't helpful) and I actually managed to go through like 90% of the game with all my Digimon always in their Rookie level. It was only when I lost a battle after battle on Millenniumon's continent (which opens up after you defeat Black WarGreymon) with already pretty strong opponents when I finally opened Youtube to check for clues and realized I've been playing it wrong, missing on digimentals, Armor evolution and insanely strong Fusion Digimon. This was also the time I decided to just watch another player finish the game and just make screenshots of it (I do not regret this decision).
The last cave on Millenniummon's continent (they're called servers) is the Moon server and this is where Ryo has to fight Millenniummon for the first time. A mysterious door appears and Ryo finds out it leads straight to Millenniummon's soul. Ken has to beat Millenniumon in his mirrored world as well and the only way to do that appearently is to beat him in the exact same turn as Ryo did (the number of Ryo's turn appears at the door) - this is crazily specific and I'm once again glad I gave up the game; it is however a great way to make Millenniummon even more sinister and powerful. Millenniummon in the Moon server is defeated and the door to his soul is open, however Ryo is the one that can access it. Upon entering Ryo's and Ken's souls are drawn to Millenniummon's dark soul. Ryo reaches a black orb that explodes when he gets to Millenniummon's castle. Millenniummon now fights as MoonMillenniummon.
As noted on Yesterday, Millenniummon is much more respectful towards Ryo than he is towards Ken, to whom he's downright rude (addressing him by a derogative pronoun kisama, "you bastard").
After they both defeat MoonMillenniummon, he disappears and Tai and Agumon are saved and can move again. Ryo, Ken and their Digimon return to town.
However Millenniummon suddenly reappears and shoots a dark spear towards our heroes. Ken jumps in front of it to save his friends and it hits him. He collapses.
He then disappears. Ken wakes up in Gennai's house and everyone is happy that he's okay. Wormmon tells us how the story continued.
The game ends but we get an after credits scene in the DigiWorld with Wormmon and Ken as the Digimon Kaiser. They're standing on a cliff possibly overlooking the Dark Ocean.
This is such a great sinister ending to the game and it links so well to season 02. Ken's flashbacks there make so much sense now and will be explored here.
Although the game is finished it still offers an extra - you can return into the game and access Odaiba through where the mysterious doors leading to Millenniummon's soul used to stand. There is a so called Kaiser room where Ryo can fight his Digimon but it only servers as a practice to Ryo, it doesn't lead anywhere storywise - Ryo never actually meets the Digimon Kaiser.