Soul Link: SANS

Please note that this isn't REALLY a fanfic, most of the story will be mine except for the part where mc has sans powers.
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In an alternate Earth where monsters have started to appear, terrorizing the general populace, with strange abilities that seemingly belong in fantasy. Fortunately for mankind, they awaken... nothing... BUT, after several years of being terrorized they develop a device name the Soul EXM Link. The strange device extracts soul fragments of the defeated monsters, then merges them with the user's own soul gifting them with the ability of the corresponding monster, if they are compatible, of course,
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Many years after the development of the link, humanity is in a struggle against a newly raising power, a lich king, named sans. Fortunately, for them, they manage to defeat him, gaining a large part of his powerful soul. Deciding to be cautious, they implant the soul into the one with the most compatibility, that being a little girl that has seemingly had a 100% affinity for undead souls. In hopes of being able to make a powerful weapon out of the girl they are unconcerned with the backlash of the implant, blinded by their excitement resulting in the girl's demise, or so they thought.
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"Why do I.... hear megalovania?" mutters a little girl, waking up in a mountain of corpses.