They don’t appear to be needed for anything extra beyond the 10 Pink Coins required to buy the Pink Key and unlock the secret boss route in Chapter 5. The remaining coins seem to be for completionists, extra purchases, or optional rewards rather than a separate mandatory unlock.

What the guides say

Recent Chapter 5 guides consistently describe Pink Coins as a currency, with 19 total in the chapter and 10 needed for the key that opens the pink door route.

So what are the extra 9 for?

  • Optional item buys after the key requirement is met.
  • Completionist collection or bonus routing.
  • Possibly future or extra uses, but that is still speculation based on current reports.

Practical takeaway

If your goal is the secret content, stop once you have 10. The other 9 are not required for the main unlock described in current guides.

TL;DR

The remaining 9 Pink Coins seem to have no required story use right now; they are mainly extra collectibles beyond the 10 needed for the Pink Key and secret boss access.