Slice of life series and films about Japanese teenagers and young adults.

possibly...

Love's in Sight! - slice of life/daily life of young people, diverse characters (FL is visually impaired, SML is LGBTQ+, ML has a facial scar, etc.) who feel alive.

Love Stories from Fukuoka 13 - slice of life about two university students, one of them deaf and the other hearing. Realistic about the barriers and common ground they find in their relationship and the leads' personalities. Not a large cast, though, since the story is centered around the the mains.

Ano Ko no Kodomo - slice of life/daily life, very realistic characters and plot of a young couple facing an unexpected pregnancy.

Daisuki!! - diverse, very realistic characters, large cast of various ages (FL is a mentally disabled young adult, the rest of the characters range in age from children to grandparents). Side romance with the brother, the rest of the story is focused on family.

I don't know if this is slice of life enough for you, but maybe #HandballStrive? Set in 2019 Kumamoto. I found the teenagers and their obsession with SNS very realistic. The film is legally available on JFF Theater until 3rd of February, for free.

(JFF Theater might be a good place to keep in mind for you, they had quite a few slice of life films in the past year.) 

 fanitha:

• Osozaki no himawari
• Orange days
• Nagi no oitoma

Thanks!

It depends on how you define slice-of-life, but from your existing PTW list I would recommend Life's Punchline for something dramatic. For a pure slice-of-life, I highly recommend Makanai. This one has more visual clues than dialogues but it is at least more eventful than let say Little Forest (if you have seen it). 

For the dramas not yet in your list, maybe you can try the following:

Gomen ne Seishun (Saving My Stupid Youth) - It's comedy in school settings with diverse characters. There will be some religious related jokes (very minor and not as far as mocking), so avoid it if you don't like that kind of stuffs. 

Timeless Love Letters to My Classmates - Bittersweet youth (school) reminiscing comedy. A bit over the top at times but overall very fun.

Aoi Honoo - It is an anime-esque comedy (so it might not for everyone) but is an adaptation of manga that was inspired from the real life story of its mangaka. The support characters are the youth version of big names in Japanese anime industries. It's amazing to think that these people alongside MC are actually from the same batch in the same University!

Kisarazu Cat's Eye - A bit havoc and maybe a bit less slice-of-life, but it's a fun drama with many characters.

Optional (may not fully meet your requirement):

Brush Up Life - MC is young adult (not so youthful) but she will hang around with friends from the school days. There will be some flashback during their youth. It's an amazing drama but I can't give a lot to avoid spoiler.

Black President - Since you mentioned Mada Kekkon Dekinai Otoko, this drama is interestingly has the same vibe with the Season 1 (2006 version). The MC however is mid age CEO but he will get involved with a group of University students. Warning that it's a bit misogynistic at some point so you know what to do if you're sensitive with that kind of things....lol

Engine - MC is young adult (not so youthful) but due to some reasons he had to live in (his father managed) orphanage among the other kids. Some of the kids are in high school age, but mostly younger.

Barakamon - MC is young calligrapher that had to deal with local bratty kids on daily basis. Not so many characters but the drama is a pure slice-of-life.

Hirayasumi - Pure slice-of-life but not many characters. Cousins live together and spend their daily life with mostly trivial things.

 RobertBobert:

@TimiZero  I was referring to any show that explores everyday life, at least in theory.

Thanks for clarifying. 

 RobertBobert:

Thanks for the post, I'll watch it later.

No problem! Check out Life's Punchline since it's already in your list!