Sqoon is an aquatic-themed horizontal shoot-em-up.
Hidden Developer Credit
Hidden in the Japanese ROM at 0x00010 is the following text. Tetsuwan Atom (by the same developers) has a similar message.
COPYRIGHT 1986 HOMEDATA ALL RIGHTS RESERVED madokakina!
A tiny copyright graphic for Home Data.
Even tinier developer names: Morikawa, Sakai, Ura, Kohama, ?, Yokoi.
This screen appears before Phase 8, the "final" level, only in the Japanese version. The text translates to: "We give up... We surrender. You're G R E A T. Oops."