しろ vs. せよ imperative forms


While browsing Youtube, I came across a comment which said the following:

> はじめしゃしょーを思い出した人は返信せよ

My question is about the ending. I understand that せよ is an imperative form of
する just like しろ. However, I was wondering what difference, if any, this makes
to the meaning of the phrase?

I found an explanation on another forum saying that せよ is more literary-
sounding, and is used in exams. However, I wouldn't have thought that a
Youtube commenter would use particularly formal language, so I wonder if
there's more to it than that.

Apologies if I've made any mistakes in how I asked the question, this is my
first time posting!




[せよ is the imperative form of the verb す](http://www.hello-
school.net/haroajapa006005.html), which is an archaic verb meaning する in
modern Japanese. This archaic imperative is still found in modern Japanese,
typically in [examinations at high school and
university](https://japanese.stackexchange.com/q/3981/5010). It generally
looks highly stiff, blunt and authoritative.

In this case, however, this せよ is used more or less jokingly, to make this
message look as if it were a military telegraph in the mid-20th century, or a
message from a boss in a spy movie (e.g., "～を抹殺せよ. This message will self-
destruct in five seconds."). Plainly saying 返信しろ would have been too rude, but
返信せよ would sound like the listeners were given a critical "mission", which
might make them excited.




[せよ is the imperative form of the verb す](http://www.hello-
school.net/haroajapa006005.html), which is an archaic verb meaning する in
modern Japanese. This archaic imperative is still found in modern Japanese,
typically in [examinations at high school and
university](https://japanese.stackexchange.com/q/3981/5010). It generally
looks highly stiff, blunt and authoritative.

In this case, however, this せよ is used more or less jokingly, to make this
message look as if it were a military telegraph in the mid-20th century, or a
message from a boss in a spy movie (e.g., "～を抹殺せよ. This message will self-
destruct in five seconds."). Plainly saying 返信しろ would have been too rude, but
返信せよ would sound like the listeners were given a critical "mission", which
might make them excited.

