This request can be found as soon as you enter Nibelheim. Next to Rydia is an older woman with a “!” above her head. Talk to her to activate this quest.
She will ask you for 3 Dragon Scales for her grandson. If you thoroughly explored the Dragon Scar dungeon that we just came from, you should already have some scales. If not, go back and grab some. I believe you can find some in a chest, and if you need more then I know it’s an enemy drop, I just can’t remember which Mirage it comes from.
When you’ve got them, go back to the lady and she’ll give you a Berserk Seed.