EDIT:
I finished the game, I just talked to the goddess in the 7th floor of the
dungeon in the right side of TOKYO district, Removed YATAGARASU from
my party (the tengu girl) and was somehow able to pass the girl that
was blocking the way to beelzebub's dungeon on the left side of TOKYO
district.
After that you need to have YATAGARASU again on your party to be
able to recruit FENRIR in your party which is on the left lower part
of beelzebub's dungeon.
Then just defeat beelzebub in the upper right part of the dungeon and
return to where the goddess is and you will be able to fight her and
recruit her.
Then on the TOKYO district go to the part above where beelzebub's
dungeon is and you will see a red dot (person) and go left from there,
you will be asked if you want to advance, say yes and a previous
boss will spawn, defeat her and head to the starting town SHINJUKU
and go the upper right part of the map...
After that try to aproach the path which leads up into a tall building
and the same previous boss will spawn, defeat her to be able to
recruit her and head into the last dungeon.
In here you will fight 3 bosses, one in each floor plus the last boss
which has 81,000 HP...
The first boss is the pregnant horned girl you fought in the beggining,
the second is the girl in a bussiness girl which has a taser on her hand,
and finally the mistress which manages the demon girl dungeon.
If you did not recruit these first 2 bosses before you can now recruit
them too, If you did recruit them before the recruit dialog choices will
not appear upon defeat.
As for the mistress you can recruit her in the 3rd floor finally, and
after that the last boss...
After notes:
The game was really fun and had that Persona-ish vibe. I decrypted
the data files and opened the game in RPG Maker VX Ace's editor, And
there is a map of japan with aditional districts like DAIBA and I think
3 or 4 more districts...
I guess future updates will continue the adventure with maybe more
demon girls and bosses since honestly speaking at the end you're given
a key item which apparently as no purpose but is related to the plot...
That and there really was no ending... You beat the last boss, exit the
dungeon and that's it for now it seems...