UG☆Ultimate Girls

Both series are about girls growing to giant size to protect the world from aliens in short format episodes. While UG has 12 minutes episodes showing each other the girls taking turns to fight, Ragnastrike shows them all fighting together in 30 seconds episodes. 

The main trio of girls have very similar chemistry and almost the same personalities. One of them is calm and composed, the other is active and unashamed, and the main character is reserved and is always afraid to fight the monsters. Each takes a different approach to their tone and the seriousness of each battle, but both are basically monster of the week shows, while diving in to romance (UG) and the psychology of the characters (Alien 9). 

If u like aliens, girls, boobies. and a single dude surrounded by 4-5 girls then you must watch this anime 

Both anime are funny. Moreover, they both have giants battling other giants, but the main different between the two is that, while one is mecha, the other is just an alien making some girls bigger to protect the town. 

Ultimate Girls is initially a Moe style parody of the Ultraman series, which is why UFO man looks alot like Ultraseven and Ultraman Jonias.