Children who are incomplete or without accessories became subject of Punishment by their parents. This can be thought as a way to protect their clan or type from being mixed with other type. But this caused them to lose variation, and brought their clan to destruction in time when it is needed.
Even with low intelligence, they could remember training from their owner to a certain level. But as soon as they are given a couple, they will quickly go against the order to "not do refreshing".
The reason is because although they remember, their priority changes.
When getting them partner, it's best to let them live separated by glass while teaching them before letting them be with each others.
In many case, parent Marisa will catch their newborn child with their hat. This means the babies' first contact with their father is in "incomplete form". So a baby yukkuri recognize their father as "something incomplete + hat