The Kris we're playing as isn't the real Kris.
The "Kris" we inhabit is the Vessel, having taken over the original's life during or via the Unknown Shelter Tragedy, intentionally or otherwise. This presumably happened years prior to our Connection to Deltarune, as this event is increasingly associated with Dess, who has been missing for a while by the time of the game's events - how and why we were suddenly 'disconnected,' not to mention 'reconnected' after so long is still a complete mystery to us.
In the ultimate twist on the themes of identity, "Kris"' desperate struggle to maintain his autonomy and overall 'self' will be called into question once he is forced to confront the human in the dark.