Trial and Error
Months passed as Rui began working on the domain technique. He took his time studying the esoteric flora of the Valley of Prisms, breaking down the manner in which the optical density of light was altered and how the changes in optical density affected the passage of light.
Simultaneously, he began trying to replicate those effects with heaven-bending. It wasn't easy. However, the foundation that he had gotten from Master Gurren was quite solid. On top of that, he also had experience with manipulating the optical density of the air in other ways when he created the telescopic technique for Master Gurren.
Unfortunately, the heaven-bending needed to magnify light was extremely different from the heaven-bending needed to halt light in its path. It was challenging, but he worked hard in trying to figure out the most efficient and effective way to make light opaque.