Listening to Kana's question, Aster was in a little predicament, normally he wouldn't mind taking them to the Rodia star cluster, Sarina was a star tribulation cultivator so they shouldn't have any problems… but that was in the past because now the sand mountain sect has set their eyes on Rodia.
So, Kana's question implied more than just saying "yes come with me to another galaxy", if Aster took them with him, then he would be responsible of their well being and although he did feel attracted by Sarina and enjoyed the adorable interactions he had with Kana, it wasn't to the point where he will take care of them like he does with his girls… yet.
