After Link has completed the Temple of Droplets, he can return to Belari to fuse Red Kinstones. This will cause a treasure chest to appear just outside the Fortress of Winds which contains a Bomb Bag Upgrade. Also after Link has completed the Temple of Droplets, he can fuse a Red Kinstone with the Minish Elder, Gentari. This will trigger Belari to start producing Remote Bombs. Link can talk to Belari to trade in his regular Bombs for Remote Bombs, and can later speak with Belari at anytime to trade back.
Belari Sprite from The Minish Cap