So in the Polycast the devs mentioned that they wanted to rework Japan, emphasizing their spiritual heritage and resilience towards outwards influence. I am proposing a unique tile improvement, called something like a shrine or dojo. In contrast to other UI, these are placed not by a worker but by a samurai, and it is a one time thing (you will receive a notification if there is a antiquity site under it, much like with settlers). It, might cost gold, but will yield quite a bit of culture and faith (+2 to both maybe), and maybe gold once something like flight is discovered. It will also increase in yield a bit over the eras/with techs. In addition units on this tile will heal for double the rate and receive a +15% bonus to defence, building it will give the samurai 10 XP. It should be quite strong, but something rather limited. Maybe by actually having a samurai to earn experience in combat before building it. As maybe a level 4 or 5 promotion. But give samurai a "receives promotions faster" promotion which is lost on upgrade.