If you have both Aster and Piyari and choose to play with them both it says "It takes a few moments for everything to register with poor Aster, and the toddler-taur looks torn between bashfulness at nearly bumping his sister-in-law, and excitement at being trapped in your lap. "Be careful," you chide, tickling his taur-tummy and waiting for him to squeal and scramble up again." Wouldn't it be half sister instead?