I need a Slice of life + Dark themes for my friend

try Fruits Basket and Girls' Last Tour

A gay romance called "Given" actually has both. It's romance, but it deals with a lot of slice of life and lots of dark themes like suicide and depression. Sasaki and Miyano is another gay drama I love - sorry, I'm into those XD - as well as Seaside Stranger/The Stranger By The Shore.

If he's alright with some science fiction, action, and philosophical ideas, Neon Genesis Evangelion is great! LOTS of dark themes, philosophical ideologies, meanings of existence, suicide, depression, anxiety, the whole work. It's the reason I went to therapy and quite literally saved my life by keeping me from committing suicide cause I felt understood!

Clannad? He just needs to have the patience to get to After Story.

Clannad
Clannad After Story

Welcome to the NHK

I haven't yet watched this one. It's on my list of 'eventual' watches. From what I've heard of it, I think this might count.
SCHOOLLIVE

Though, like Invocations suggested, I think Girl's Last Tour would probably be the best fitting example.

Sayonara Zetsubou Sensei is the first to come to mind, though I'm not sure if that is what he's looking for...? It's a comedy, but it is, you know, about suicide.

If you want something more serious with an episodic nature, maybe MUSHI-SHI? xxxHolic (and CLAMP's works in general) also has a weird balance of comedy/slice of life style things and dark subject matter. I would also say anything directed by Kunihiko Ikuhara will tend to have a weird balance between those two tones, and I am always suggesting people check out his work.

Hope those help a little! Good luck finding something :D

Hmm, sounds more like he's looking more for a romcom with satire/ecchi rather than a dark SOL, but I'll try to recommend both! Hopefully these are not too dark/sad

1. Call of the Night

• Genres: Romance, Slice of Life, Psychological, Comedy, Supernatural
• Themes: Insomnia, Societal Expectations, Freedom

Call of the Night

2. The Magical Revolution of the Reincarnated Princess and the Genius Young Lady

• Genres: Yuri (Girl x Girl), Romance, Slice of Life, Comedy, Isekai
• Themes: Envy, Emptiness, Reincarnation, Magic

The Magical Revolution of the Reincarnated Princess and the Genius Young Lady

3. Don't Toy With Me, Miss Nagatoro

• Genres: Romance, Slice of Life, Comedy
• Themes: Girl Teases Guy, Tomboy, Tsundere

DONT TOY WITH ME MISS NAGATORO

4. Violet Evergarden

• Genres: Drama, Slice of Life, Psychological
• Themes: Rehabilitation, War, Female Protagonist

Violet Evergarden

5. Anohana

• Genres: Slice of Life, Drama, Romance, Supernatural
• Themes: Tragedy, Hikikomori, Coming of Age

Anohana The Flower We Saw That Day

Haibane renmei aka the best anime ever if you are coping with grief

Fruits Basket 2019
A Silent Voice
NANA
Kageki Shojo

Well, I am actually surprised how well this fits. 10/10 would cry again.
Les Misrables Shoujo Cosette