To become an ancestor you must die with survivng same-gender descents or heirs who still remember the name of and recognize their descendance from either you, or an ancestor older than you up your own line of gender-inheritance. Families who can remember far back down their ancestral lines keep the spirits of very ancient ghosts alive, for when an ancestral spirit is forgotten, or the ancient ancestor which anchored them is forgotten, then the ancestor itself simply ceases to exist.
The ancestral spirits, or ancestors, exist alongside us in a dim, colorless reflection of our existence, as untouchable, immaterial incorruptible, naked images