Short for Enjo-kosai , meaning "compensated dating." In media, this specifically refers to transactional relationships between adults and minors.

While there is limited information available on this specific topic, it appears to be related to a program or initiative focused on preventing junior high school girls (13 years old) from dropping out of school or becoming disconnected from education. The term "Enko" can be translated to "to go off the rails" or "to derail," suggesting that the program aims to prevent students from straying from their educational path.

Mami saw the impact of this discovery on Yui and decided to create a memory book together. They spent the next few weeks gathering stories, photos, and other keepsakes, installing a shrine of sorts in the backyard to honor Yui's parents.

Given these terms, here's a speculative write-up: