About Seiji Chihara

That's right.
If you call yourself a monk, then you are a monk.

This is true of everything.

You are free to call yourself, but in reality, studying Buddhism is still necessary in order to gain trust from others, including qualifications and licenses appropriate to that.

Details of Mochimon Seiji are unknown, but realistically, what is announced through the media is that he probably performed a “tokudo (ceremony to enter the Buddhist sect)” due to a relationship with a master and monk (master).

Even though I became a monk to do this ceremony, I would like you to take this ceremony as if you had joined the ranks of monks.
There are various sects in Japanese Buddhism (Jodo sect, Nichiren sect, Shingon sect, etc.), and training is required in order to receive qualifications and tests according to the regulations of that sect.
There are also many temples that do not have an independent sect.
However, when funerals etc. are actually requested, they are often asked to sects with traditional forms, and they probably want to request a safe and secure denomination or monk.

People commonly referred to as chief priests all have “teacher” licenses. (Teachers registered with the Agency for Cultural Affairs)
Seiji is also associated with the Buddha and has now become a monk, so I wonder if he originally had personal connections. Buddhism is steep and strict, but they probably got started after including that.

There are self-proclaimed monks in the world who do not belong to any temple, and apparently monks who have never practiced ascetic practices.
People who do alms and the like don't even know where they belong.

If you don't have the mindset to take advantage of people's weaknesses and exploit money etc. with the power of religion, it won't be a particular problem.

Buddhism is difficult, but the more you learn, the more you know that you are ignorant.
The teachings of Buddhism, which have continued since the Buddha in 2500, allow us to live in a state of mercy where we are structured so that we can save ourselves while saving people.

Gassho

Basically, a disciple of a Buddhist monk can call himself a Buddhist monk.
So, if you go back to the monk's mentor's mentor, it's likely that you'll end up with the Buddha.
Becoming a monk, becoming an apprentice to a master and monk, and receiving a kaimyo (Dharma name) is called kudo, and those who have received kudu are registered as monks of each denomination.
At that point, he is in the same state as Ikkyu-san from his childhood, who is familiar from picture books and anime, so he still doesn't have a teacher qualification (qualification to become a chief priest).
In order to qualify as a teacher, it is necessary to complete the curriculum stipulated by each denomination and complete necessary training.
Note, even if you don't become a monk and remain at home, you can receive a kakana (Buddhist name) if you receive a prescribed ceremony, and they often perform a ceremony to give them a kakana when mourning someone who was not a monk, but in that case, you are not registered as a monk.

I took a look at your question. Certainly, I think monks also have stages. Basically, “tekudo” is the first in the Shinshu sect, and that is equivalent to becoming a monk. In other words, leave the secular world and become a monk. Next, you will obtain a qualification called a “teacher,” and this requires a qualification to study at a university or the like. Simply put, this means being able to speak the Dharma. I think this system is because it would be difficult to be taught the law without knowing Motoyama's intentions at all. If I just became a monk, that would be enough, but my image is that of a little boy. You're probably in a state where you become an ascetic monk. The way of thinking is probably different depending on the denomination, so this is probably not the case, but just for your reference.

A “monk” is not a national qualification, nor is it something that local government chiefs approve, and the position of being a monk of the ○○ sect of traditional religious groups is certified only within the ○○ sect. Speaking of extremes, there is no difference from private sector qualifications such as “○○ sommelier level 2.”
The existence of the ○○ sect or ○○-ji as a religious corporation is certified by the country or local government, so there is public backing, but “becoming a monk of the ○○ sect” itself is just private.
So if anyone is alone without belonging to any denomination, then one day they suddenly declare, “I am the founder of the supreme Buddhist sect in my life, and I am a monk,” there is no reason to deny that itself.

In the case of Chihara Seiji, it seems that he was officially taught by the Tendai sect, which is a traditional cult, so it seems that he is not “just saying it.”
There are differences in degree between each denomination, but basically anyone can “earn” a degree and become a monk of that religious group. However, in order to have a temple and become a chief priest or actually carry out missionary activities, it is necessary to have the knowledge and experience necessary for that purpose. Whether or not you meet those requirements as a monk of the ○○ sect is checked and approved by each religious group, it will be practically difficult to continue your activities.
Anyone can get a driver's license for a car and become a paper driver, but it may be a bit similar to the fact that knowledge and experience are necessary to actually continue driving safely and securely.