This page explains how to start and complete the Little Sister's Big Request side quest.
How to Start the Quest
Go to South Akkala Stable, which is northeast of Akkala Tower, and talk to Jana, who is sitting by a tree.
How to Complete the Quest
For this quest, you need a Cold Darner, Warm Darner, and Electric Darner. Warm Darners can be found near South Akkala Stable where you receive the quest. Cold Darners and Electric Darners can be found in the Hyrule Ridge area, which is near Ridgeland Tower.
When you have one of each, go back to South Akkala Stable and talk to Jana, then Gleema. Talk to Jana again to receive a reward.