Board Thread:Episode Discussion/@comment-4141313-20181229081856/@comment-26146765-20181230021709

Gundam Legilis wrote:

We see Merc punch of all things (probably deciding to adapt his training regimen), and the fact that he had a Semblance, but his daddy stole it from him. Which raises the question, how is it even possible to have a Semblance that steals manifestations of other people's souls? Maybe the abuse was what "stole" his Semblance?

If a Semblance is a manifestation of someone's soul, then Marcus abusing Mercury could've actually been terrible enough that Mercury was affected to the point where he was unable to use his Semblance. Semblances are manifestations of a person's innate and personal power, so if Marcus made him feel powerless/weak or whatever to an extreme, Mercury might have been mentally affected to view himself that way permanently/near-permanently and therefore could not use his innate power.

Similarly, on American Horror Story, the relationship between mother and daughter witches Fiona and Cordelia functions this way, with Fiona's abuse towards her daughter making her feel magically/physically/mentally incapable and supressing her innate magic. Assuming Semblances work the same way, manifesting as one discovers or realizes that they have inner power, if Mercury was made to feel extremely useless and powerless for a long time, he wouldn't be able to manifest a Semblance.

Of couse this is Mercury Black we're talking about, who does not seem to have any self-esteem/self-confidence issues, but in any case this is my take on it.