Note The first two and last two episodes of Level E are quite mild and have very little to report about as far as averse content. As the series progresses towards the middle, the themes and language become more and more of an issue. Also, this is a review of the Funimation English dub of the series. The brief amount of the series that I watched in subtitles appeared to have even more language issues than the dub.

Violence / Gore:
The series does not show a lot of actual bloodshed. Usually it is in splatters on the ground, or else you see aliens bleeding (but their blood is blue). There is a point in which a man's silhouette is shown getting stabbed through the head. Also, a woman shoots three men, but the screen blacks out as she shoots. One episode shows a boy preparing to eat the flesh of a girl's corpse. After, he is shown licking his blood-stained hands. There is less-violent monster fighting during a few episodes. Some characters get kicked/punched pretty hard. Oh, and a scene in which we see a dead-looking body shoved into a trash can. The image is shown multiple times.

Nudity / Sexual Content:
One character mentions that it is, "normal for people to have multiple sexual partners throughout their lives."
A main character cross-dresses for almost an entire episode; a monster reads a sex-book during the same episode, and asks the cross-dressing character some questions of a sexual nature. Though nothing actually happens, there is mention of teacher/student sexual role-play.
One scene shows two bugs mating. Mention of an alien "STD."
A girl is shown in the shower from behind, and part of her breast is shown. There is a naked female silhouette in an episode. A guy sees a girl's breasts while spying on her and comments. A couple of female characters are shown in bras/undies. A woman takes off her shirt in front of a group of young boys.
A square-shaped monster gets knocked down to reveal what appears to be genitalia and pubic hair. A chibi-looking character pulls a missile out of his pants.
A female character tries to have relations with another female. A girl grabs another girl's exposed breast. Spoiler: A girl's gender is changed so she can mate with an alien. It is mentioned that although biologically female, that the girl is a male "deep down."

Potentially problematic theological themes:
Joke about offering a boy as a human sacrifice. Mention of alien "evolution" a few times (not sure whether macro or micro evolution). A man wearing a cross necklace is portrayed as possibly being high. One character swears "on all that is holy." One character is called a "demon king".

Other potentially problematic themes:
Other than the first and last two episodes, this anime is full of mild profanity (even on the fringe of deeper vulgarity at times).
Mention of a perfume "so strong it'll make you high." One character is often seen smoking a cigarette.

*Level E starts out innocently as the story of a high-schooler having to deal with an unwanted roommate. The series breaks off of that completely on a few random tangents before arriving back where it started. Though at times humorous, Level E often winds up being crude and at times vulgar. It is most certainly not intended for young audiences.