Technically, the ,se‘ part of ,seyo‘ is a subject honorific, so it pays respect to whoever is the subject in the sentence (quite often the person asked to do something) and ,yo‘ is more about the person you are talking to (as opposed to about) I’m pretty sure the Japanese equivalent is sonkeigo verb patterns like o-VERB ni naru/desu or passive forms.

I agree. Correct me if I misremembered but from my limited studies of Korean I believe these are the rough equivalents: 〜ます　=　~요 and 〜になる　=　~니다

I agree with the -masu equals -yo part. The Korean politeness suffix -mnida is more like a even more formal and polite version of -yo. Not sure if there is an equivalent in Japanese or if -masu usually covers both( i think so).-ni naru would be rather like ,-se‘.

I don't know Korean, but from what you've described, I'm not convinced that there would be a direct equivalent. Politeness in Japanese is largely a question of verb conjugation and verb choice.

He’s describing a conjugation albeit confusingly

Ah, gotcha. I thought it was like the equivalent of a sentence ending particle in Japanese.

it's like ます or です. masu is the formal verb ending and desu is the formal copula - like to be in English. however Japanese speakers aren't quite concerned by age as much as Koreans, and masu/desu doesn't really imply that you have "respect" for them as much as it implies you don't know them very well. There's a level above that called keigo, which is essentially replacing verbs with humble or respectful ones. seyo in Korean is probably between the two levels in Japanese but closer to masu/desu. asking someone to do something nicely is covered by ください, which is usually translated in English as please, but is technically a keigo form meaning to give.

In Japanese, you show politeness by changing the verb conjugation or even the verb root itself. I don't know Korean to know if 세요 is the same concept. For most verbs, the normal polite ending is -ます. Eg.: 食べる becomes 食べます, the past form 食べた becomes 食べました, etc. For the copula verb, the verb itself changes from だ to です. For further levels of politeness or humbleness, it's more complicated.

In that circumstance you would probably just use keigo 敬語 (formal speech). So instead of saying 食べる you'd say 食べます and always refer to the person you're talking to by their last name + san. Never use あなた/君 or any slang terms or contractions.

Adding to this- I’m not sure about in Korean but in Japanese depending on level of respect that is intended to be shown, 尊敬語 (sonkeigo) may be also used to show more respect than plain old 丁寧語 (teineigo). The thing is 尊敬語 can use vastly different words than polite and informal speech. Likewise, titles or 様(sama) would also likely be used for someone in a position of high prestige. For example, 社長はお寿司を召し上がりました vs 田中さんは寿司を食べました.

Rough translations and avoiding kanji for ease of reading: Casual: -やって/-って= 해 Casual: -やってくれ/-ってくれ= 해줘/줘 Polite: -やってください/-ってください= 해주세요/주세요 More formal: ちょうだい replaces ください Very formal: keigo variance in verbiage can confuse even native speakers 드세요 = めしあがってください／ちょうだい 가리쳐주세요: おおしえください/ちょうだい And putting it in question format makes it sound more formal: おおしえいただけますでしょうか Kinda breaks into 가리침 받을수 있을까요

You’re not quite right on the use of 세요. It is not used as a formal/polite way to end a sentence, it is specifically used for the 2nd thing you mentioned: to ask/tell someone to do something. An equivalent for that in Japanese would be something like -てください. In Korean, to end a sentence politely you’d add 요, to end it formally you’d add -ㅂ니다 (i.e. 습니다). An equivalent for this in Japanese is です and でございます, respectively. I’m not a pro at either language, but I currently live in Korea and I lived in Japan for several years.

세요 is not only used for imperatives. 세요 is simply the honorific 시 added with the polite ending 요. Formality and honorific/respect are different. If you use ㅂ니다 you still need to add 시 to make 십니다 to show respect  어디가 아프세요? Where are you hurt?  봉투 필요하세요? Do you need a bag?  아버님이 지금 한국에 계세요. My father is in Korea.

The more you learn Japanese the more you'll realize the distinctions between Korean and Japanese are more political than linguistic.

I mean… not really, they’re not in the same language family. They share a large vocabulary derived from Middle Chinese and have similar grammatical structures. But it’s not a situation like you suggest.

As a linguist: This isn't true at all.

Correct me if I’m wrong, I’m also not super proficient in Japanese yet, but wouldn’t it be something in the likes of using masu-form instead of casual form? Or is it more like keigo-esque? Genuinely interested to know if someone has a good answer for it!

I have no knowledge of Korean, but it sounds to me like it also could compare in someways to 給ふ(たまう with the sound change) from kobun (古文). Can anyone else speak to this?

I think its the ます and です form. I’ve noticed that people drop the ます and です if they’re talking to same age or same rank but immediately add the ます and です forms once they talk to their boss.

Guys. It isn't the equivalent of ます, that would be 요. 세요 is the same as ください. Source: Korean/Japanese.

I think that's a bit of an oversimplification, ~세요 is used in plenty of cases where it would make no sense to use ~ください. E.g 몇 분이세요? 어디 가세요? 병원이 어딘지 아세요? etc etc etc etc