After three years of waiting for Guardians Of The Galaxy Vol. 2, we've all been wondering about Peter Quill's parentage, and what this means for the wider #MCU. Vol. 2 delivered this information with more than its fair share of shocking then horrifying twists, sending poor Peter (and much of the fandom) reeling. As we knew before the movie was released, Ego — a.k.a. the Living Planet — is Peter's father. But what we didn't know is that Peter was just one of many hundreds of offspring sired by Ego on his megalomaniacal mission of conquest. And then he killed all of them, except Peter, draining them of life force and leaving their bones in a dusty pile inside his planetary structure. Yikes.
But what if another of Ego's children survived? That's the question posed by Redditor JMH1982, and they have an intriguing theory...
Is Mantis Really Peter's Sister?
This actually makes a lot of sense. Mantis' backstory was left purposefully vague — all we know is that Ego found her in her "larval state", abandoned on a planet, and rescued her.
However, the later revelation about Ego's true intentions casts doubt on this. He certainly feels little regard for those he deems lower life forms, and as he is so focused on his grand mission it seems unlikely that he would save such a small being. Enter the theory:
Considering [Ego's] motivations in the film, how he came across Peter's mother and all of the other women in the Galaxy, not to mention his tendency to use his offspring for his own means ... is it possible that Ego lied to Mantis all this time (It's kinda what he does with his children) and that she was his daughter. Without the ability to produce the light that Peter can, he kept her alive for only one reason — she could help him rest and recharge.
I think she is a child of Ego and therefore Peter Quill's blood sister. Something I don't think he's aware of. But will be a necessary component in the future.
This is an excellent theory, and one which explains a few unanswered questions from the movie concerning Ego's character. To develop this line of thought further, we'd have to assume that Ego altered Mantis' memory: From the size of the skeletons Gamora found, it seems that Ego reconnected with his children when they were in their early adulthood, as perhaps their maturity allowed them to produce the light — or not, as it turns out.
It's highly unlikely that Ego expected Mantis to produce the light as just a little larval creature, so perhaps when he decided to keep her around to use her empathetic ability, he used his telepathic powers to rewrite her history.
However, there are some issues with this theory. Firstly, if Mantis really is Peter's sister, then it would make more sense to reveal this in Vol. 2, as this movie dealt with the Ego plot. Carrying this revelation over to Vol. 3 would reduce its impact, and the threequel would be burdened with reminding us who Ego is, what his plan was, and why we should care that Mantis is Peter's (possible) sister. And of course, this isn't the only option for Mantis' heritage.
Though it's almost certain that Ego didn't tell Mantis the whole story, it doesn't necessarily follow that she's his daughter. Perhaps, knowing of her race's empathetic abilities and needing someone to help him sleep, Ego stole the larval Mantis from her family, then lied to her about her past. That seems more in keeping with his character than her alleged rescue.
Either way, we'd like to see Mantis discover the secrets of her past in Vol. 3. It would be nice for Peter to discover another blood relative after the deaths of his mother, his real father, and his surrogate father, and some development of the relationship between Mantis and Peter would be interesting. But overall, we're excited to see Mantis realize her identity in Vol. 3, after a lifetime of isolation and lies — whatever those lies may be.