I’ve read a few VNs in Japanese but its hard to give them a precise difficulty rating. Most of the stuff I’ve read that is on this site seems to be in the low/mid 20s so its hard to get a feel for the upper difficulty of things but I’ll estimate the best I can.
生命のスペア - L23
Inochi no Spare | vndb - This was the first VN I ever completely finished in Japanese. There’s a few medical terms in here but overall the reading was pretty easy. Honestly by the end of it, it was starting to get boring with how often they repeated some phrases and whatnot in the narration portions. The sentences were pretty short overall too.
ネコぱらExtra 仔ネコの日の約束 - L18
Neko Para Extra: Koneko no Hi no Yakusoku | vndb - This VN is really short and has no serious plot. Just raising some “kittens”. Its fine if you like cute slice of life stuff and the scenes are pretty short so you can pick up and read whenever. Can’t think of anything difficult about this VN.
月の光 - L22
Tsuki no Hikari | vndb - The nice thing about this game is that it is fully voiced and I mean fully voiced. All of the characters and narration is voiced, so you could put the whole thing on auto mode if you wanted to and play it in the background for listening practice. The game is mainly a slice of life romance type thing. None of the vocab is hard but some of the sentences in the game are longer than what I normally find at this difficulty level.
Monkeys!¡ - L32
Monkeys!¡ | vndb - I love this VN so much. It is definitely a VN that I am going to try and re-read in a few years when my jp is better. I think my biggest problem difficulty wise with this VN was the huge number of unique words (11,025 unique words compared to something like the Bloom Into You spinoff novels with 7,239 unique words). So there would be some sentences where it felt like I knew none of the words they used. They also had a lot of weird analogies and stuff related to food that went over my head.
But with that said, there was a lot of slice of life dialogue that was pretty straight forward. Its one of those games where the difficulty spikes back and forth a lot depending on who is talking. All the girls are お嬢様 but to different degrees so they have their fancy way of talking.
推しのラブより恋のラブ - L26
Oshi no Love yori Koi no Love | vndb - I don’t have too much to say about this game. It was just okay. Its about a girl (the MC) who is obsessed with some edo-period gacha. While she is obsessed with that, there is another girl who is into the MC and is trying to date her. Most of the difficulty for me came from gacha and otaku terms used in it (the MC is a huge otaku).
クロウカシス ～七憑キノ贄～ - L26
Caucasus ~Nanatsuki no Nie~ | vndb - A murder mystery game set in an old-mansion. I thought this game was going to be super hard before I played it but the ease of the game surprised me. Maybe its because of the setting but everyone speaks very “proper”, I can’t really think of any slang or anything and that made it very easy for me to read it. There was one huge info dump scene that was kind of hard to follow but outside of that, it’s relatively easy. One of my favorite “murder mystery” games. I highly recommend it.
LOOPERS- L25
LOOPERS | vndb - I read this with the WK VN club. Story-wise the VN was, uh, not my favorite but I think is a decent VN to get into reading with. Most of the sentences in this game are rather short, I think most of the difficulty comes from the characters all having different styles of speech so there is a lot of slangy stuff in it.
オトメ＊ドメイン - L27
Otome * Domain | vndb - This is a pure slice of life story which is okay. I usually love slice of life but I found it hard to be that attached to any of the characters. This is another game that takes place at an お嬢様 type school but the girls in this aren’t too formal. One of the main heroines is actually a huge chuuni and half the time she talked, both me & the MC were left thinking what the heck did you just say 
ふゆから、くるる。- L32
Fuyukara, Kururu. | vndb - The best way to describe this game is that it is insane, crazy, all of those type of words. If you read spoilers on this game you might not even believe they are real because of how crazy the plot can be. Having said that, the game is really fun for the most part. Most of the difficulty comes from there being a lot of really long sentences and that the things the characters say can be so weird that it makes you question your understanding, as in did they really say that or am I reading this wrong. The game also gets really philosophical at times and I struggled a lot when it came to that.
