Intensity = 4, PURPLE
All activities and full nudity as long as no genitals are shown (impossible, you say? Keep reading!) Titles with this rating will most likely depict intercourse in progress, explicit masturbation, oral sex, mutual/manual stimulation. Teenage to adult characters, or siblings.

NOTE: There is an artistic convention in doujinshi of partially obscuring or "smudging" the genitals (or in some cases apparently drawing then erasing them.) Genitals that are clearly "present" but masked by clothing, body parts, sheets, text balloons, circus tents, or other graphic elements will not count as "visible."

To Reviewers: Here's where it's difficult to give clear review guidelines, so if there's a penis and you're rating something a 4 instead of a 5, give some explanation. One other possible criteria could be number: if there's 1 or 2 in a 40 page book, give it a 4 and mention that. If on the other hand, there's a smudgy penis on every page, please note that in the review and let's call that a 5, OK?

To Readers: Conversely, if you're looking to buy a title rated level 4, be aware that the dividing line between 4 and 5 isn't crystal clear.

How strong could it get? Aside from what's mentioned above? Pretty much the full range of sexual activity, including fisting or rimming (again, as long as genitals are not fully/clearly drawn.). Here is a place where a detailed review of the specific activity that earned the rating could be useful.