The society of an ancestral guardian community has been built around keeping something guarded, and all other aspects of that society have been shaped by the need to do so. Whether that is guarding that thing from the outside world or the outside world from the thing can vary, but in either case, a certain sense of responsibility and vigilance has sunk down to the very bones of your society.
Ancestral guardians value reliability, responsibility, and cooperation, borne out of a strong sense of social responsibility. They tend to form close-knit, cooperative communities. They tend to be stoic, hard to deceive, and very forthright communicators.
Sometimes the weight of their charge can breed bitterness and even paranoid xenophobia with any outsider seen as a likely threat, but it is more common for these communities to be warm and compassionate with a strong pro-social regard for not just their own members, but those of surrounding communities as well.
Characters raised in the ancestral guardian culture share a variety of traits in common with one another.
Long Watch. You gain proficiency with the Perception skill. You also gain an expertise die on saves to avoid suffering levels of fatigue.
Sentry’s Arsenal. You gain proficiency with a single martial or rare weapon of your choice and light armor. The choice of weapon often reflects specialized armaments needed to keep some specific threat in or out.
B.S. Detector. You gain proficiency in the Insight skill with a skill specialty of sensing motives.
Languages. You can speak, read, write, and sign Common and an additional language of your choice.