Mr. Driller G, alongside the rest of the main cast you may know well by now, introduces Usagi, Ataru's rabbit-like buddy. What you may not know is that after unlocking him in the PS1 release, completing his Mission Driller levels shows not the expected arcade cutscenes, but a set of images explaining how the two met!
While their origin story is touched upon in the Drill Land lore cards, the site admin believes this to be the most in-depth retelling due to its visuals. Because of this, they decided to put it on the site and include a basic translation which pulls context from other Driller media.
BANG!!!!!
On that fateful night, a meteorite crashed into the forest. When Ataru rushed to the scene, he found a rabbit sprawled out on the ground.
Ataru rescued the rabbit, passed out and injured, and tended to its wounds.
The rabbit woke up later, in the middle of the night. In truth, it was not a rabbit, but an alien sent to take over Earth! Its first thought was to attack Ataru, but...
The rabbit decided world domination could wait, as Ataru's kindness lead it to want to observe the human race. With that in mind, it joined him in his travels.
To reach the conclusion of the story, you have to beat all four Mission Driller stages again after already having to beat North Pole once. With the Live Select code and Usagi's busted skillset, it's not actually that difficult, but it's still a bit tiring after save scumming through it once.