The episode bundled with the 13th volume is about the Sumo competition that held at Tempest for the first time, suggested by Rimuru.
The three-part OVA bundled with the 14th, 15th, and 16th manga volumes is an original trilogy written by Fuse.
Rimuru has been teaching Shizue's students at Ingracia Kingdom's Freedom Academy. The time has come for the school's annual outdoor training event, where the students will test their combat skills in the field. Rimuru is determined to win the competition and take home the prize money, but he is challenged by Jeff, an honorary teacher who sees Rimuru as a rival. The competition is underway when suddenly an unexpected enemy appears!