Finn Balor
Finn Balor defeated Seth Rollins to become the first ever WWE Universal Champion, but ever since, Rollins has enjoyed far more success.
Seth Rollins doesn't really need the Intercontinental Championship, and losing it to Balor will allow more focus to be placed upon the erstwhile Demon King.
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This one is easy to book.
Have Seth Rollins hold an Intercontinental Championship open challenge on RAW, after a grueling pay-per-view match.
Have Finn Balor beat a depleted Rollins, clean in the middle of the ring, and have Rollins shake his hand after.
This allows Rollins to lose in a protected manner.
Have Rollins be attacked by Braun Strowman and pals after the match.
The next week on RAW, have Balor come out and offer Rollins a rematch whenever he wants, as soon as he is one-hundred percent. Have Rollins come out and say that he will accept Balor's rematch, but only after he is done dealing with Braun Strowman and company.
This allows Balor to stay a babyface, and prevents either man from taking a loss in a rematch.