I have to say I didn't find any errors with grammar or characterization. :)

This made me feel all fluffly inside. :3 It was super sweet, and I just loved Dante's and Kalas' interaction. Although they weren't the main center of attention, their characters didn't feel intruding on the Vergil and Sagi intimacy. :)

Yeah, your style definitely improved! Well done! You saw for yourself that you can do it, fool! You thought you couldn't. Stop underestimating yourself!

I never thought that the twins could live together and learn to get a long (to some extent). I don't say it's bad; the idea is just new and refreshing! I also think it's believable (I presume they must have gone through a lot of things before they could be like this).

What I found especially interesting is the striking contrast regarding Sagi. First we see in the digression, Kalas' walking in on him and Vergil having sex. Poor boy; was all stunned. Then we see how Sagi sleeps with a hand in his mouth, like a baby. Which one is he, innocent or naughty? I wonder...Definitely tells you're making him a complex character.

There are still some repetitions, but it is alright. It's much better than before, and I believe that more practice would lead to better results. You're on a good way.

There were two mistakes I noticed, which would be the indefinite article a/an: "a elderly", and also, you missed some commas when addressing people. Other than that, your grammar is brilliant, as always.

Keep up good work, Kai-chan!