Yes, those are butt handles. To pilot the mechs in this anime it requires two pilots. A boy and a girl. The girl has to ride up front, in an awkward position, while her male partner rides in back and controls other aspects of the mecha via butt handles.
Oh, it looks as silly as it sounds.
Another weird part of this series is the utterly strange design of the mecha. Robot looks like a lady. These things are powerful in battle, but it's hard to not just think they're ridiculous with huge anime eyes on each of them. Let's not forget they seem to have boobs or robo busts too.
Then you have some other weird circumstances, like only kids can pilot these mechs and some basic knowledge about the world is missing. I mean these kids don't know what a kiss is. The world has weird monsters in it. Everybody lives in mobile bases. And some weird organization is in control.
I haven't even gone over the main characters, but let's just say the people who made this have seen Evangelion.
I'm only giving you a taste of how strange this anime is. DARLING in the FRANXX will continue being a wild ride as it has a 25 episode season and the dubbed was at episode 8 last time I checked. Give into those pervy tendencies if you want to watch