UFO is essentially a puzzle game with adventure elements (navigating a character). The hero must travel to different rooms in the apartment building at different times, trying to snap the perfect picture of the invisible alien. The player is given a time limit and a picture limit (ten pictures per visit). Afterwards, the hero has to return to Mother, who will eat the negatives (really), produce pictures, and then decide whether they are suitable or not. Each successfully taken photo opens a new area and/or a new time of the day in the apartment block.

In July 1999, the newest Cosmobus "Daima-O" crashed into the third planet Earth in the Chahaya system.

Earth is a frontier planet that does not belong to the Galactic Federation.

The 50 passengers are lost in a side-hole dwelling that the Earth people call an "apartment.

The cause is believed to be a stall due to engine trouble, but due to "certain circumstances," rescuers must be cautious.

The passengers in distress are invisible to the naked eye due to electromagnetic waves and CFC gas, so the player, as a rescue team member, must take pictures with a cosmo scanner to determine the time and location of the passengers' presence, and rescue them one by one.