There are eight hidden developer credits that when entered into the High Score rank board will cause that row to display a flashing rainbow effect:
•KISSY = Yoshihiro Kishimoto, Programmer
•TAKKY = Yukio Takahashi, Designer
•MAKO. = Satou Makotoshi, Unknown Role
•JUNKO = Junko Ozawa, Composer
•YURI. = Yuriko Keino, Composer
•FIGER = Unknown
•NKGT. = Norio Nakagata, Composer
•WATAB = Unknown
Contributed by MehDeletingLater
According to a 2007 interview with the game's planner/graphic designer Yukio Takahashi published in the book Game Shokunin, the interviewer commented that the ending scene where the main character removes their helmet to find out that she’s actually a woman was the first game to make such a surprise twist. He responded:

"This was influenced by the anime Nausicaa of the Valley of the Wind. Actually, a bunch of things were influenced by Nausicaa: the protagonist you just mentioned, the side-profile perspective of the paccets, and the Blue Worm boss… Also, as I mentioned, because people during the development were so enthusiastic about slaughtering all the paccets they could, as a contrast to all that cruelty I wanted at least in the final scene to have something cute and adorable, so I drew those ending images."
Contributed by ProtoSnake
According to an interview with the game's planner and graphic designer Yukio Takahashi in the book 'Game Shokunin', it took him a whole year to finish off development of the game. He had to do everything but the programming himself, and drew all the graphics in about 5 to 6 months.
Contributed by ProtoSnake
Kissy's real name was revealed to be Masuyo Tobi when she appeared in Mr. Driller. Her name is a play on the Japanese phrase "Toby de arimasu yo" which means "I can fly".
Contributed by Mass Distraction