Twelve-Winged Dark Seraphim
I highly doubt Zhou Wen is a Companion Beast of Earth. The biggest reason why is that Prisoner would have noticed. Prisoner IS one of Earth's Companion Beasts, and he didn't think Zhou Wen had much relation to him besides being Zhou Lingfeng's son. There's also that child switch Zhou Lingfeng mentioned, which suggests An Jing might be the true special child, and such the true Earth Companion Beast. Prisoner wouldn't have met her because Ouyang Ting doesn't visit his family much, so she could be the one he's been looking for. If she really is that individual though, it means her mother left the Lost Immortal Sutra for her to use, but it ended up with Jing Daoxian somehow. That means an accident must have occurred, even though The Thearch claims there were no mistakes.