I have vague memory of a Beelzebub manga, where Furuichi visists the underword years after the events of the last chapter and there we see a grown up Lamia, and both Furuichi and Forcas comment on how she has developed on the right places, well Furuichi is commenting about her breasts and Forcas about her behind but that's not directly mentioned. So was it some kind of a fever dream or is it really something that existed at some point.
I presume it's either in the one of the extras that we get sometimes at the end of a volume, or it's from Beelzebub Maou Gaiden, Beelzebub Extra.
According to https://kaguya.live/manga/details/66729/beelzebub-maou-gaiden there should be 5 stories
Contains:

• Beelzebub
• Ōmiya Jet
• Nirai Kanai Yori
• URA BEAT
• Beelzebub Extra

the middle 3 are one-shots that have nothing to do with Beelzebub, the first one is the pilot chapter 0, and that only leaves Beelzebub Extra. But I can't find it anywhere on the web anymore, because google removes it from the results.

So if anyone knows about this I would like to confirm and if possible give some proof about it.