“Second Star” refers to the legend of Brave Vesperia and the Child of the Full Moon. His sword is actually an extension of Estelle, which is why he feels so comforted with it.
Yuri is generally sociable, but only if someone takes the time to meet him.
The ToV ending happened, but his blastia is back while in the world of Tumblr.
He likes to banter with Flynn and Judith, but he gets more competitive around Flynn.