The process of getting the special Partner Ribbon in Pokemon Scarlet and Violet isn't as difficult as you might think, especially if you've already completed the main story of The Indigo Disk DLC. This particular Pokemon ribbon is, according to the game itself, "a special Ribbon awarded to a Pokemon that was once partnered with another great trainer."
Acquiring the Partner Ribbon therefore requires you to trade Pokemon with one of the Special Coaches in The Indigo Disk. This requires a little time hanging out with the coach in question before trading is made available, and some coaches require additional tasks to be completed before you can have them visit you at Blueberry Academy.
Regardless, obtaining Pokemon from Special Coach trades will result in the creature having the special Partner Ribbon and a unique title that corresponds to the coach that traded it to you in Pokemon Scarlet and Violet.
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How to unlock all Special Coach trades in Pokemon Scarlet and Violet
To get a special Partner Ribbon in Pokemon Scarlet and Violet, you'll need to trade with one of the Special Coaches in The Indigo Disk DLC. The coach in question must be invited to the League Club three times to enable trading, but some coaches have special requirements before you can unlock and invite them to the League Club.
The full set of Special Coaches in Pokemon Scarlet and Violet can be found below, complete with the requirements to unlock them and which Pokemon they'll trade:
Once you've met the unlock requirements for the Special Coach of your choosing, simply invite them to the Blueberry Academy League Club room three times. You'll then unlock the ability to trade with them, and regardless of which Pokemon you receive in the trade, you'll notice it has the special Partner Ribbon attached to it.
All of this is incumbent on the fact that you've accessed Pokemon Scarlet and Violet's Indigo Disk DLC, as Blueberry Academy and the League Club room won't be available otherwise. Moreover, if you haven't beaten the stories of The Teal Mask and The Indigo Disk DLCs, you can't access the Mochi Mayhem epilogue and unlock coaches like Arven, Penny, and Nemona.
Contrary to popular belief, you don't need to battle any of the Special Coaches via the League Club room to unlock the ability to trade with them. As long as they've been invited to the room three times, the trading option will unlock. However, you may want to consider battling the Special Coaches anyway, as they can provide some great rewards like Herba Mystica, Rotom Phone cases, and clothing items.
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