This is the weirdest Saturn disc you'll find. UNO DX Special Edition isn't really a soundtrack, it's a novelty disc with greeting messages from Seifuku Koujou Iinkai (a real idol group from the 90s) plus three answering machine messages.
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That's it. Four tracks of idol group voice content bundled with a card game. The 制服向上委員会 greeting is basically a promotional intro, and the 留守電メッセージ tracks are literally voicemail recordings you were supposed to think were cute.
Peak late-90s Saturn bonus disc energy. No actual music to speak of. If you collect obscure Saturn extras or 90s idol crossover gaming stuff, this exists and that's kind of the whole point.