Let me break down what you'll get for helping those lost gestrals find their way back to sastro (they're quite lost, which is why finding them is so rewarding). For the third one you'll receive 3 chroma, which is actually pretty valuable since it helps with those early-game upgrades. The eighth gestral is hanging out on a flying island north of the crows, and returning this one gets you a unique hairstyle - might not seem like much but these cosmetics are actually quite rare.

When you manage to track down the ninth one near the night sanctuary (southeast of sirene), you'll unlock something really special - the retreat picto ability. This is a game-changer because it lets you instantly escape from battles when things get too intense.

The real reward comes from finding all nine though - you'll get both an achievement and some pretty useful exploration abilities that make getting around much easier (especially helpful if you're planning to go for 100% completion). Just remember that some of these gestrals can be quite tricky to spot, so taking your time to explore each area thoroughly is definitely worth it. A good tip is to listen for their distinct sound - they make a unique chiming noise when you're getting close.