It would seem to be possibly Starry Knight related.
Shouma appears to be using the “Starry Knight” Deck (with Strong Jukyu using Lyrilusc). In it he uses two Starr Knights to make an Xyz Summon.
A Rank 4 Xyz Monster. Stats and effects currently unknown. It appears to require 2 Level 4 monsters, but further restrictions are unknown. Its name appears to be Sterling Knight, playing on Starling (the bird) and Sterling Silver (an alloy), that appear to have the same etymological roots.
The main reason to also bring this up is more likely than not, this will be the next major promotional card to come with Structures’ next physical volume, considering the tendency of the manga to debut new cards before a volume goes on sale.