This year, Aa video caused quite a stir on social media in Japan.

no need to capitalize it because there's a comma.

The video is about a conversation between a famous entrepreneur and a former Fuji TV announcer Mr. Hasegawa exposing the toxic work environment within Fuji TV.

space after a period in abbreviations

Mr. Hasegawa stated that a sexual- tribute- scheme existed ion Fuji TV, where female announcers were expected to entertain and socialize with higher-ups.

space after a period in abbreviations
hyphens should not be used between words unless it's a compound adjective before a noun

Shockingly, he himself had experienced being offered to a famous gay Japanese celebrity Osugi by his senior announcers Mr. Kasai and Mrs. Sasaki.

comma

As the gathering broke up, Osugi subtly exchanged glances with Mr. Kasai and Mrs. Sasaki.

comma

Mr. Kasai said to Mr. Hasegawa "Hase (his nickname in short), that's how it is".

Mrs. Sasaki said to him with a smile "That will be for the diner".

And then Mr. Hasegawa and Osugi got on the next elevator.

and then he continued, "The moment the doors closed with a 'whoosh' and a 'clunk', he forced a tongue bath on me.

Mr. Kasai denied the allegation on his blog but Mr. Hasegawa flatly refuted his claim, stating that he has kept a daily diary since he was 16.

He recorded the incident in it, which could serve as an evidence.

I thought keeping a diary canould really help put an end to those 'he said, she said' arguments.

since this is a past thought

Explaining theOPTION A: Describing a Controversial Whistleblower Video in Japan¶
OPTION B: About a Controversial Whistleblower Video in Japan¶
OPTION C: A Controversial Whistleblower Video in Japan

オプション C は簡潔です。このオプションをお勧めします。

OPTION A: This year, Aone video caused quite a stir on social media in Japan.¶
OPTION B: This year one video caused quite a social media stir in Japan.

Theat video is about a conversation between a famous entrepreneur and a former Fuji TV announcer. Mr. Hasegawa exposinged the toxic work environment withinat Fuji TV.

Mr.HasegawaHe stated that sexual-tribute-scheme existed inat Fuji TV, wherein which female announcers were expected to entertain and socialize with higher-ups.

He further claimed that at Fuji TV there'has a deep-rooted culture wherein which female announcers are seen as "carabet hostesses" in kyabakura.

carabet hostesses --> カラベットホステス

For those who are unot familiar with Japanese culture and kyabakura, it is a type of nightlife establishment in Japan whearabet culture, customers pay to spend time with "hostesses" who engage in conversation, pour drinks, and create an entertaining atmosphere.

ALSO POSSIBLE: .... and create a sexually-charged atmosphere. (....性的に興奮した雰囲気を醸し出します。)

While there may be a flirtatious element,s, overt sexual activity is not part of the service offered at a kyabakuracarabets.

LOGIC: It might be useful to distinguish between "covert sex" and "overt sex."
Covert sex can consist of innuendos, hints, or flirting. Overt sex involves bodily contact. 「隠れたセックス」と「公然のセックス」を区別することは有用かもしれません。隠れたセックスは、暗示、ヒント、またはフラーティングから成り立つことがあります。公然のセックスは身体的接触を伴います。

Shockingly, he himself had experienced being offered as a "joy boy" to a famous gay Japanese celebrity Osugi by his senior announcers, Mr. Kasai and Mrs. Sasaki.

He shared his past experience: "The four of us went to eat at an Italian restaurant.

As the gathering broke up, Osugi subtly exchanged glances with Mr. Kasai and Mrs. Sasaki.

Mより慣用的に:r. Kasai then said to Mr. Hasegawa, "Hase (his nickname in short), that's how it is".This is how the game works."

This is how the game works = This is how things operate. = これは物事を行う慣習的な方法です。

私の推測：Mrs. Sasaki saiwhispered to him with a smile, "ThatYour services will be focover the diner costs.".

He went on, mentioning that "I had no ideas what they meant at first."

andThen he continued, "The moment the doors closed with a 'whoosh' and a 'clunk', he forced ahis tongue bath onto me.

Mr. Kasai denied the allegation on his blog, but Mr. Hasegawa flatly refuted his claim, stating that he has kept a daily diary since he was 16.

He recorded the incident in it, which could serveCOMMENT: Diary entries might not hold up as an evidence in most courts.

I thought keeping a diary can reallymight help put an end to thoseany 'he said, she said' arguments.

This year, A video caused quite a stir on Japanese social media in Japanthis year.

social media in Japan -> Japanese Social Media: smoother way to say it.
[this year] to the end: smoother phrasing.

The original sentence is fine grammatically, this is just a more natural way to state it. The only problem in the original sentence was the capitalization of "A", which shouldn't be capitalized, and the comma after "this year", which is not necessary

The video is about a conversation between a famous entrepreneur and a former Fuji TV announcer Mr. Hasegawa exposing the toxic work environment within Fuji TV.

a former Fuji TV announcer -> former Fuji TV announcer: getting rid of "a" makes it so that Mr. Hasegawa is specified as the "former Fuji TV announcer" that we're interested in.

Mr.Hasegawa -> Mr. Hasegawa: missing space

Mr. Hasegawa stated that a "sexual- tribute- scheme" existed in Fuji TV, where female announcers were expected to entertain and socialize with higher-ups.

sexual-tribute-scheme -> a "sexual tribute scheme": we're missing the article "a". Also, we should be putting the phrase sexual tribute scheme in " ", and not hyphenated as sexual-tribute-scheme suggests it's an adjective, and "sexual tribute scheme" suggests it's a noun that was quoted.

I got this from a hard-to-reach place. ◎
I got this from a "hard to reach place". △ <- only works in very specific contexts where you're quoting someone who said this to you
He said that place was "hard to reach". ◎
He said that place was hard-to-reach. X

He claimed that at Fuji TV there'has a deep-rooted culture where female announcers are seen as "hostesses" in kyabakura.

at Fuji TV there's a -> that Fuji TV has a: smoother way to say it.

While there may be a flirtatious element, sexual activity is not part of the services offered at a kyabakura.

service -> services

Shockingly he, Mr. Hasegawa himself had experienced being offered to a famous gay Japanese celebrity Osugi by his senior announcers Mr. Kasai and Mrs. Sasaki.

him -> Mr. Hasegawa: The pronoun "he" is referring to something that is confusing as it's too far away in the entry. We state Mr. Hasegawa for clarity

He shared his past experience: "The four of us went to eat at an Italian restaurant.

[] -> of us: Assuming that Mr. Hasegawa was amongst the 4, "of us" is necessary here for the pronoun.

As the gathering broke up, Osugi subtly exchanged glances with Mr. Kasai and Mrs. Sasaki.

Perhaps sensing something,Then the two seniors took the elevator first, like they had planned this in advance."

Perhaps sensing something -> like they had planned this in advance: "sensing something" is more of a non-planned, in the moment type decision, but it's implied here that this decision seemed to have been preplanned, so we change the phrasing.

Mr. Kasai said to Mr. Hasegawa "Hase (his nickname in short), that's how it is".

Mrs. Sasaki said to him with a smile "That will be for the diner".

Then the elevator doors closed with a 'ding' right in front ofin his face.

right in front of his face -> in his face: rephrased as "in his face" is more forceful and emphasizes the happening better.

And then Mr. Hasegawa and Osugi got on the next elevator.

This sentence should be appended to the previous:

Then the elevator doors closed with a 'ding' in his face, and Mr. Hasegawa and Osugi got on the next elevator.

He wentMr. Hasegawa said "I had no ideas what they meant at first."

We have to restate "Mr. Hasegawa" here because the pronoun is unclear on whether it's pointing to hasegawa or osugi. The quote should also be continued in its full form, you can see the reasoning below in the next correction

and he continued, "The moment the doors closed with a 'whoosh' and a 'clunk', he forced a tongue bath on me.

The moment the doors closed with a 'whoosh' and a 'clunk' -> The moment the doors closed: Japanese has a lot of words imitating sounds (onomatopoeia) to describe things, but English doesn't, and in almost all cases doesn't use it as an adjective like Japanese does. We say "the doors closed" and that implies the rest of the sentence.

and he continued -> X: "and he continued" is often used with quotes that are extremely long, but this quote is not extremely long, so we can get rid of it and just continue the quote in its full form.

Mr. Kasai denied the allegation on his blog but Mr. Hasegawa flatly refuted his claim, stating that he has kept a daily diary since he was 16 and recorded the incident, which could serve as evidence.

The next sentence is appended to the end of this sentence to make it more logical.

He recorded the incident in it, which could serve as an evidence.

I thoughtink keeping a diary can really help put an end to those 'he said, she said' arguments, so it's good that he did..

It seems you're drawing (positive) judgment on Mr. Hasegawa's diary keeping skills, so we change it from past to present (thought -> think), and state your opinion on the matter.

He went "I had no ideas what they meant at first."