This was a one-shot (no sequels) game for the Nintendo DS. This page has ALL spoilers, right away. If you have not played yet and don't want to spoil, stop now. Because of the console's limited capabilities, character creation options were limited. Conversations are all text, and it's mostly anime-cell looking art. The visual style of PSO mostly hangs around, so you can tell it's certainly a game from the series.
This portable game for the DS tells the story of what happens on Coral AFTER the Pioneer 2 leaves.
Your character has to help solve the mystery of the newmen from the moon & help to defeat Mother Trinity, a device invented to help clean up the planet-wide disaster on Coral.
Because the game is smaller, on a hand-held, there isn't the gigantic roster of relevent & irrelevent NPCs that other games have had, and the plot is presented in a fairly straitforward manner. Missing entire branches (example: Kireek) via accidentally skipping obscure stuff isn't going to happen with this game.
Online component:
It did have an online component, but it was hampered by Nintendo's "Friend Code System" - you had to actually know & arrange ahead of time who you were going to play the game with. Does that completely defeat meeting new friends? Yes. Unless you traded giant secret numbers via the PC or in person (where you are allowed to speak or write) you couldn't play with other people.
Some online-only content did exist.
A few special arenas & stage areas could only be gotten to online, however, it didn't really add anything to the plot of the game.
Various characters join your party to help you solve the mysteries of the plot. There are also non-active characters as well, who hand out missions or provide exposition.
Hidden Character Statistics:
There is a hidden “Affection” stat that each of the play-with-able NPCs has for your character. You raise or lower it with the dialogue choices. It can be VERY difficult to control because some of the dialogue choices are nearly the same thing twice like “Watch out!” vs. “Look out, an octopus!” You’d think they’d both do the same thing but they don’t AND the result is hidden. The game also makes it very easy for Sarisa to dominate all the affection stats unless you’re constantly miserable to her because of the sheer number of quests they assign her with you. (Yes, you can choose other characters, but only the assigned character gets any dialogue options…and thus hidden affection points in story quests)
Keep in mind also that being agreeable toward characters leads to more info, dialogue and positivity while being rotten doesn’t help much plot-wise. The character that has the highest of this hidden stat at the end of the game (when you beat the final boss) will re-appear to you with more to say. To obtain all of the "special ending dialogue" means you would have to beat it 4 times, each time cultivating a different character into liking you.
PSZero Plot Write Up-
Learn the entire plot of this game, written up as a kind of story summary. It varied a little depending on which race you chose at the start. (Your character's origin & how they show up at the start of the plot.)