There a few people who is able to answer to ask that what “Obosan” is. Obosan is called as “Sou” or “Souryo” and it specify to a person or group who retire into Buddhism. Basically it name does not matter the number of people in Japan.
After the age, Souryo classified depends on their class and role. The top “Dai Sou Jou” to the lowerst class “Kobozu”, these calls “Sou” or “Obousan” as same.
And person / group who practice and spread the Buddhism, also calls as mentioned.

A familiar example, a Souryo who takes care of a temple calls “Jushoku” (most common Obousan for Japanese who lives in and maintain a temple). This Jushoku means a role which has duty to spread and keep Buddhism.

The main role of Obousan are the following; sutra recitation, ascetic practices, ceremony, ceremonial occasion (coming‐of‐age ceremony, marriage, funeral, festival), Buddhism mass, grave management, spread Buddhism, etc.

Have you ever heard a word “Zazen”?
One of the denomination of Buddhism, try to reach to the origine of mind by doing Zazen training.
It calls Zen denomination and Zen Sou.
They put importance to spread Master spirits, Buddhism secrets and Buddha’s mind by human spirits to human spirits, not by word of written form.
The most important in here is spirits.Zen is complicated and there are more than 30 definitions.One of the most easy to understand spirits is “Zen is the name of Spirits, and Spirits is the body of Zen”. Well, it is still elusive expression. It could say “You are Zen and it’s in your spirits”. What is a spirits? It seems like it not saying about human emotion, it wants to say about more essential part like its part and duty. In Buddhism, it says Buddha mind, and based on the idea a spirits exist even in a tissue paper. Tissue paper’s part and duty is to absolve water, remove uncleanness and a computer is really useful (and it also has spirits) but cannot clean a place. Everything has each part and duty for existence.
There is a short story as the following. A famous priest of Kamakura period found a tissue paper on the floor and he picked up. He said “Ah, I found a dropped Buddha”. Some people say this is the spirits of Zen and spirits which is includes by the universe which is Buddha mind is Zen.“Zen is the name of Spirits, there is nothing which does not have spirits so practice Zen is to learn from you”. And this continues to “go to the beyond to you”.Really difficult……

One of the ways to reach to the beyond to you, there is “Zen Mondo”.
Zen Mondo is one of the training to achieve enlightenment. If I say easy way, it is a riddle. However, the question which uses for Zen training, there is no logical answers which contains absurdity. And it says if a person keeps considering about the question for years, someday will comes out a spirits and achieves enlightenment.

There is a story about this Zen Mondo.
An emperor asked a Sou “I order to build so many temples, how much will I receive blessing of god”. And the monk just answered “nothing (if the emperor forgets to get blessing of god, the number of blessing will be uncountable)”.

Actually, there is not a correct answer in Zen Mondo. Find your answer by considering.