Long running series featuring ginormous oversized breasts, like Saki, Haiena-chan ni Nerawarete, Ano Toki Tasukete Itadaita Monster Musume desu and Kaii to Otome to KamikakushiWhen asking for big breasts people usually say something as big as a mango to be 'big', while that is certainly true in real life, for anime/manga the bar, for me, is way higher. At least comparable to the torso they are attached toBasically I want to read more stories featuring characters as big as Lucoa 5714u

Asobinin wa Kenja ni Tenshoku Dekiru tte Shittemashita? ~Yuusha Party o Tsuihou Sareta Lv99 were the first two that came to mind...

~4400 manga completed
~1700 ongoing...

I've been following Chichi Chichi for a while, and I've tried reading the second one but couldn't get far, not even the breasts saved it for me.

Someone in another place told me about AniList Large Breasts tag

Saki that started normal and went full bananas (or rather, watermelons) on breast size. (And I mean bigger than the second one you recommended)

I fear series that started off normal and changed over the years like Saki are not really searchable, I've found it by pure chance

Maybe not as extreme as the previous ones but what about Zyugoyas manga tend to have huge boobs...

Edit: Also just ed Hen na Chishiki ni Kuwashii Kanojo: Takayukashiki Souko-san

Edit 2: And Tensei Colosseum - Saijaku Skill de Saikyou no Onna-tachi o Kouryaku shite Dorei Harem Tsukurimasu

Edit 3: Not sure how I could forget about Ataerareta Skill wo Tsukatte Kasei de Isekai Bijotachi to Ichaicha shitai...

~4400 manga completed
~1700 ongoing...

Big tits coliseum is great

i cannot believe eiken was ignored

Adding Isekai Koushoku Musou Roku - Isekai Tensei no Chie to Chikara wo, Tada Hitasura XXXX suru Tame ni Tsukau to the list...

~4400 manga completed
~1700 ongoing...

I filtered my lists using the Big Breasts tag and picked out some for you. Some of these are very popular and you probably know of them already. Sorry if not all of them are as big as you were looking for lol

Uzaki-chan wa Asobitai!

It's quite sad how rare such manga are. Unfortunately it seems everyone that draws the really massive breasts just make porn instead. Which makes complete sense but still very saddening. Most of the examples are just at the level of Big Breasts, barely some get to Huge breasts.