So! FM and UM, often referred to as FU or FUM, was an INCREDIBLY experimental iterator. Largely because half of their purpose was not only trying to solve the Great Problem, but also solve the problem of the rains that were starting to drown places. To do this, they ended up making a very, VERY odd iterator.
FM was an iterator built to, quite literally, WALK to find what they need. His can is a quite small one, forced to try to cut down on weight to be able to move. Due to her size, she actually doesn't even reach over the clouds, and instead has been heavily reinforced to deal with it. However it was BECAUSE he couldn't reach the clouds that UM was made and proceeded to be plonked down right on top of him.
UM, as you might imagine considering the name, was an iterator built to FLY. The idea for her was, more or less, to gather and recycle the clouds to let them out in much smaller bursts so less rain would form. She is also built to have massive wind power that allows her to blow entire storms in a different direction. Her cloud gathering was also an integral part to FM, as the two are connected and the water she takes in is also used to power him.
FUM was,,,,,not that big a success. It worked a bit, but in the end it wasn't enough to make any more like them. Normally this would get them shut down and taken for parts. HOWEVER. Despite not fixing the problem, FM specifically was an INCREDIBLY serious and devoted iterator. She took the job very seriously, and despite all the oddities of the structure, was one of the most devoted to finding the triple affirmative period. UM not as much, but she was a very big part of FM and the two could not work without each other. The ancients decided this devotion was a good enough reason to keep them going, so while they could not built any cities on top of them or anything, they kinda just. Let the two go.
NOW. Personality wise? These two are disliked by many, and it is,,,,,rlly not for no reason. FM is an incredibly serious, workaholic, callous, and kinda mean iterator. His immense devotion has not petered out in the SLIGHTEST despite the ancients being gone, completely believing that it doesn't matter and they need to fulfill their purpose, ancients or not. Generally does Not Care what other people think or what they are doing. Also frequently steals people's water, and does not care if you are ok with that or not. FM is also equipped with canons and other combat things to use against predators that try to attack them, and have used these things to quite literally take out probably a non zero amount of iterators. Despite being generally cordial, FM is beloved by nobody.
UM meanwhile is a catty, gossipy, flamboyant, reckless, generally bitchy kind of gal. Also kinda very creepy. Loves to get in other people's business, doesn't care what they think, and is incredibly manipulative for no real reason other than liking having control. Unlike FM, she thinks finding the solution is a useless waste of time, and will actively have fun sabotaging work anybody is doing, including and specifically FM's.
As you can imagine, the two are polar opposites. And, frankly? They hate each other's guts. They frequently threaten each other with mutually assured destruction, FM threatening to shoot down UM, and UM threatening to just fly away with all the water. They work shockingly well together, but are constantly at odds. This is not helped by the fact they share a lot of amenities like overseers, experimentation chambers, and such things like that. Both are convinced the other will kill them, and honestly they are correct. UM thinks FM is a uselessly devoted hardhead workaholic, and FM thinks UM is a stupid conniving waste of space. Both love to get on each other's nerves, and half their time is spent sabotaging the other in various petty ways. Unfortunately when they work together they do AMAZING work, and give stupidly good advice about various things like water conservation and stuff like that which they will surprisingly tell you willingly. Whatever the case, they are very fucked up and skrunkly. Open for questions if anyone cares to!