Is the artist depicting Tani Takeshi and Mizuki's Characters?

That was my very first thought as I saw the thumbnail. I'd say the probability is very high. Pixiv might offer some clues, but Google translate just makes it into word salad.

Mizuki-san isn't named specifically in the tags, but the whole karaoke set-up, plus a tag indicating respect to a variety of artist, makes it a practical certainty. Tani-san, on the other hand, is definitely mentioned by name.