What does にして mean in this sentence (a variant of にしておく)? 感傷にひたるのはこれぐらいにして

Question

I've come across this sentence (internal monologue) in a visual novel:

感傷にひたるのはこれぐらいにして、階段を下りたらいつもの遠坂凛に戻るとしよう―

What confuses me is the これぐらいにして part. As for これぐらい, I assume it's the second meaning from here, i.e. used to make light of the character basking in her sentimentality. As for にして, I don't think it's either of the two meanings listed in my grammar book - (1) a compound particle to stress simultaneity and an element of surprise or (2) a conjunction meaning "and".

Rather, it would make more sense as a variant of にしておく, i.e. leaving as is. Lit: "leaving this sentimentality thing as is, let's get downstairs and return to my normal self" What I'm asking, then, is: does it look like it? Am I missing something big here?

Here's Tohsaka's monologue bit that precedes it:

わたしは学園で一番の優等生でありながら、誰かの一番にならないように波風立てずに生活している。それが、まあ、こんな風に疲労している時、なんとなーくつまんないなあ、と思ってしまうワケなのだ。「っと、もう時間か」ホットレモンを飲みきって立ち上がる。感傷にひたるのはこれぐらいにして、階段を下りたらいつもの遠坂凛に戻るとしよう

(by the way としよう here is just a volitional of suru with a to particle, right?)

Answer 1

Seems to me that you are reading a little too much into the phrase.

「(Noun) + は + これぐ(or く)らいにして」 is a very common expression meaning "Enough with (noun)".

The 「の」 in 「[感傷]{かんしょう}にひたるの」 nominalizes the verb phrase 「感傷にひたる」= "to sentimentalize over something", so it can be treated like a noun.

Grammatically speaking:

「これぐらい」 means "around here", "about this much", etc. What that refers to is the fact that the speaker thinks s/he has already done a sufficient amount of sentimentalizing and s/he now wants to call it quits and move on. In other words, 「これぐらいにする」 means "to bring something to an end".

I am a bit surprised by your analysis of 「～～にして」 here because it is only the te-form of the verb 「する」. You do A first and move on to do B.

A: quit sentimentalizing (right here)

B: go down the stairs and get back to my usual self as 遠坂凛

「～～にして」 is not always a variant of 「～～にしておく」, but in this context, it just so happens that you could replace 「にして」 by 「にしておいて」 or 「にしておき」 as far as grammatical correctness and meaning. The author's choice 「にして」, however, sounds better and more natural.