it's a storage application. really really wish they had put out the Platinum update but I mostly remember this game for the Gallade-Chikorita Wars my sister and I would wage using a copy of Pearl and Action Replay where we'd spawn in one of the two Pokemon and try to have as much of them in as possible
This game is so cozy! I loved importing my Pokémon and seeing them interact with each other and do silly things. However, I can understand why most people don't like this game, since it's really pointless and it functions as a subpar storage service, but I still have fond memories of it nevertheless.