If I remember correctly, the ??? refers to the MC's inner conscience. In other words, the blindfolded, purple-haired girl that you can visit from the bed. She is the only character who gives advice for helping Asuka. I hope this helps.
Try sleeping on Sunday, then visiting the MC's conscience through the bed. The bed has different options, and one of them takes you to a realm where you can speak to your conscience and even visit an alternate version of the Demon Slayer universe.
