ถึงฉันอีกคนในโลกนี้

You must receive a Trailblaze sticker from the opposite Gender. So if you're Stelle, ask your Caelus friend to send you a Trailblaze sticker. There are exactly two Trailblaze sticker, titled "Melon" and "Shake".

A reference to a chapter of the storyline in Honkai Impact 3rd. - Credit: tsuyoon