Oi mecha fans. Im looking for an old manga with mecha i was reading some years ago - myb someone can help.

The facts i remember:
- story is in a big city with lots of highrise buildings
- mechas are as big as 20+ story buildings
- characters transform into mechs
- losing an arm in a fight means the arm is also lost in human form
- different weapon types such as rockets and swords
- contains explicit nude and sex scenes (one scenes with two lesbians, one scene with a (bad?) guy fucking a random girl)
- some of the mechas protected a joung child, the child could also transform into mecha but destroyed a lot more than the others
- uncolored, double the size of a normal manga book