Selena is Princess Luna
Selena is implied to be related to Blueblood (Celestia's nephew), but outranks him and seems to have significant government authority as well (she wasn't asked for a ticket at the Sleepy Oaks train). Selena enters Songnam as Jericho leaves it, just when they're expecting a Princess. She's familiar with ancient songs, hasn't been addressed "Miss" or "Ma'am" in ages, tenses up when her name is compared to Luna's (same meaning), spaces out at the implication of parents, and laments that the moon doesn't get much notice. Now, she may just be totally obsessed with it because it's in her name, but it's a whole load of "coincidences" that wouldn't be necessary for the story. The fact that she has cyan eyes only strengthens the connection. The Blue-Eyed Lady is also Princess Luna
Jericho only seems to run into Blue-eyes when Selena's somewhere far-off (and only AFTER Selena scrutinizes him and gets interested). Plus she, like Luna and Selena, has blue eyes and behaves a bit towards Jericho like Selena does, albeit it far more mysteriously and aloof. Cards is related to Blackjack in some way.
Same manestyle, coat color, EXTREMELY unlucky... seriously, they HAVE to be related in some way....