TheMy collab partner iswill be 柊優 (Hiiragi Yuu,) the host VTuberwho will host.

They are not just any streamer though, they are really big, I mean, t. They have tons of followers on their Twitch and Twitter.

The collab is about thatwill focus on Yuu-san and the audience teaching me, an English Learner, English word/meme/internet slang, etc.

I think that Llanguage learners would enjoy this.

I am so glad that they suggested me this collab to me first.

I guess I doidn't have the guts to suggest any collab to them.

No, it's not about mythat I didn't have the guts.

The use of "my guts" in your original sentence is unnatural. Although "have the guts" is a phrase used to describe courage, the word "guts" cannot be used for that meaning elsewhere.

The collab partner is 柊優 (Hiiragi Yuu,), the host VTuber.

They are not just a streamer, they are really big, I mean, they have tons of followers on their Twitch and Twitter.

凄いですね！

The collab is about thathow Yuu-san and the audience teaches me, an English Learner, English words/memes/internet slang, etc.

I think that Llanguage learners would enjoy this.

そうですね。

I am so glad that they suggested me this collab to me first.

I guess I don't have the guts to suggest any collab tos with them.

The collab partner is 柊優 (Hiiragi Yuu,) the host VTuber.

We wouldn't really say "host VTuber", we would say the collab was going to be on their channel.

They are my number one favorite streamer.

Use of "they" as a neutral pronoun is controversial. Older people will sometimes require he or she or use "he/she" if the gender is unknown. Younger people are more likely to use "they" as a neutral pronoun or if the gender of the person is unknown.

They are not just a streamer, they are really big, I mean,; they have tons of followers on their Twitch and Twitter.

Also, they are really popular, talented, and kind.

The collab is about that Yuu-san and the audience teaching me, an English Learner, English words/memes/internet slang, etc.

I think that Llanguage learners would enjoy this.

I am so glad that they suggescontacted me for this collab first.

The most common phrasing would be that they contacted you for the collab, or that they reached out to you.

I guess that I don't have the guts to suggest any collab towith them.

No, it's not about my guts.

This weekend, my first collab as a VTuber is going to happen!

sentence is correct - emphasizing "this weekend". If emphasizing that it's your first collab - My first collab as a VTuber is going to happen this weekend! - may be better.

The collab partner isI will be collaborating with 柊優 (Hiiragi Yuu,), who will be the host VTuber.

future tense; collab partner is understandable, but a little unnatural.

They are my number one favorite streamer.

number one and favorite sounds redundant

They are not justNot only are they a streamer, but they are also really big, I mean,popular, as in they have tons of followers on their Twitch and Twitter.

not only...but also; ("a ton" - if more formal)

The collab is about thawill be about Yuu-san and the audience teaching me, (an English Llearner,) English word/s, meme/s, internet slang, etc.

future tense (this weekend); used parentheses to minimize the use of commas and to not distract from the rest of the sentence; used commas for listing

I think that Llanguage learners would enjoy this.

I guess I don't have the guts to suggest any collaboration ideas to them.

"any collab to them" sounds a little awkward