Here is my video guide to all three starlight upgrades, starting for this one.
1. Get 10 blood crystals from around the map before doing this.
2. Go to the beach, to Danchi.
3. On a catwalk there is a tunnel that leads to Crimson Acid (use CTRL to find her, or whatever the Xbox controller button is to detect where people are).
4. Talk to them, and select "Starlight Upgrades"
5. Buy the cosmos upgrade for 10 blood crystals.