Hikikomori Princess Marriage summary:

The strongest “confined” Lady has appeared! The Debutante Ball — a party organized by the kingdom where nobles who have turned 17 are invited. In the corner of the glamorous venue, lays a mysterious wooden box that did not fit the atmosphere. Approaching the box that everyone in the room was wondering about was the second prince of the kingdom, Syphon. With eyes filled with curiousity, Syphon examined the box thoroughly. But then, a voice is heard from inside the box…?! “Umm… Is there anything you need…?” A sensational love story between an introverted, (physically) confined noble lady and an inquisitive, lively prince! (Synopsis: Gourmet Scans)