In one episode, girls are shown swimming at the pool. The is clearly intended to provide fan service.

Season 2 Episode 1 has a scene of a female character showering and her ass can be partially seen.

The first season has some fan service in it, though the second and third have less, and focus more on the plot of the series.

Some romance, but nothing sexual.

Some school related bullying.

A character is punched over and over again in the face, causing him to spit blood. In the scene, the ground is shown stained with drops of blood. This scene is repeated twice, first time is the original scene in the (2nd season) and the second time is a flashback, a part of the scene is shown (season 3).

Mild language.

Around the same level of profanity as a show like My Hero Academia or Naruto, with only 1 or 2 uses of "damn" or "hell" every episode. Some episodes have none at all.

Profanity is mainly used for adding more personality to the characters, so some (like the protagonist) swear rarely or never, while there are some other characters (mainly boys) who do curse regularly.

Mild language like "damn" and "hell" throughout with periodic uses of "bitch"

None

A teacher is shown smoking a cigarette in season 1.

There is a scene showing a party and some students appear to drink some alcohol.

Rated TV-14 for mild violence and mild language.

Most students have a backstory explaining their personality and behavior in the show. Some, if not most, of those backstories may be disturbing (suicide, bullying, depression, solitude, stealing, and many more).

Some callous and reckless people are shown in the show. It may be frustrating to watch these characters behave however they want without repercussions.

Despite the show being an anime and sometimes lighthearted, it is very realistic in portraying people's personalities and weaknesses. All characters are absolutely different from each other, and many portray traits of trauma or personality disorders.