For a Better Reunion is the third part of Aranyaka: Part II - Dream Nursery and covers the final preparations for Festival Utsava.
How to unlock For A Better Reunion Sumeru World Quest in Genshin Impact
You can unlock this World Quest by completing the following prerequisites in the Aranyaka: Part II - Dream Nursery questline in this exact order:
Once both are done, you'll automatically unlock For a Better Tomorrow, starting with paying a visit to Rana.
How to complete For A Better Reunion Sumeru World Quest in Genshin Impact
Follow the quest marker to Rana's location near Devantaka Mountain. Interact with her to prompt dialogue with Paimon and the Aranara. Arana states that he'll be staying to protect Rana and won't be able to attend Festival Utsava, so he gives you his flower in advance. He'll then ask you if you'd like to head straight to Vanarana, respond with Let's go. This will teleport you directly to Vanarana, where the next World Quest called Festival Utsava will automatically begin.
Check out our Genshin Impact Even Beasts Stumble World Quest guide to complete other quests in Sumeru.