Gacha

Even if I pull on the pickup, I can't raise them.

If you're free-to-play, it's wiser to save your diamonds for specific strong characters rather than going for Platinum. Especially the Star Guidance gacha after clearing 17-4 is highly recommended due to its high certainty. Using Fin's precious resources in the most efficient place is the correct answer, ho!

If it's for a point-earning campaign, you should probably raise them since there's a deadline, but I think it's also an option to just pull for the platinum ticket amount or friend gacha amount and aim for Destiny and Guidance.