When I Gained Invisible Power, I Want to Enjoy Everything

One day, the protagonist overhears his mother and younger sister talking in his room. His sister has disliked him since childhood, and their conversation makes her grievances clear. After their talk, the mother leaves, and when the protagonist emerges, his sister's angry voice rings out—forcing him back inside. While venting his frustration, his phone rings with an unknown number. Dismissing it as a scam, he nearly hangs up when the call suddenly connects on its own. Confused, the protagonist eventually hangs up, missing the caller's final words. Realizing he hasn't eaten, he reluctantly leaves his room to face his sister—but to his shock, she seems unable to see him. Was that mysterious phone call real? What supernatural change has occurred?