Btw is there a tag for deep kisses?
There is Lots of Kissing, which commonly involves deep kissing, but not always.
Btw. for a recommendation of a seriously lewd manga with lots of raunchy kissing, see After School
I second that, After School is amazing. Talk about a relationship based on kissing! The two lead girls try kissing one day and they just can't stop. And they didn't know each other and hadn't even talked to each other before that day! And from then on they meet every day just to have hot kissing sessions.
(And I remember things go on like this for months before one day one of them suggests they should become....... friends! Out of a vague sense that kissing so much when they are not even friends is like....... somehow improper, no?)