User blog comment:KodachiZero/Chain Chronicle V3 on the Wiki + Q&A/@comment-122.55.57.66-20161125094300/@comment-3215051-20161125100303

Initiation skills are a little tricky to explain. We barely understand it ourselves.

It looks to me like you can equip a character with relationship level 10 to a version 3 hero character with relationship level 10. Then you will be able to use the former's skill through the latter one when a specific condition is met in battle. [Zero]