Xevious has a hidden target on the ground, called the Sol. It appears only if you drop a bomb on one exact spot. Masanobu Endo, who designed the game, said in a 2003 interview that Namco did not really understand the point of hidden characters like the Sol. So, in his words, he told them 'oh, that's a bug…' and snuck it in.
He was born in Tokyo in 1959 and studied at Chiba University. By his own account he arrived at Namco right after Rally-X had been released. Sources disagree on whether that was 1981 or 1982, so this story does not pick a year. At the time he was drawing sprites, the small pictures that move on an arcade screen. Programming was also fun to him, he said, so he learned it on the job.
The order for Xevious came from the marketing department. Konami had just put out Scramble, and Endo's team was told to make 'a 2-button scrolling STG,' a shooting game with two buttons. That is a plain request for a copy of what was selling. He took it, and he asked for more than it said.
In 1983 he said he wanted to give a video game, for the first time, a consistent world and setting. He also said he wanted to avoid making a game where humans fight each other, because a modern war setting brought too much mundane realism. So Xevious has no soldiers. You fly a ship over a land of strange machines, with one hidden tower on it that nobody at the company had asked for.
The game opened in Japanese arcades in early 1983, and players took it apart quickly. Endo recalled in a 2014 interview that only two weeks after release he heard someone had counterstopped it, meaning pushed the score counter until it stopped. Years later he named one regret about Xevious: a player could keep going forever on a single 100 yen coin.
His next game was The Tower of Druaga, released in June 1984. It has sixty floors. Each floor hides one treasure, and each treasure appears only after a particular action: defeating a set number of enemies, say, or entering a joystick code. Some treasures are needed to finish the game, and missing one can leave the game unwinnable. The game never says any of this.
In Japan, players began leaving notebooks beside the cabinets in arcades, filled in by hand with hints and small drawings for each floor. Regulars came back to read them and to add what they had proved. Nobody could find all sixty treasures alone, and the notebooks were how the strangers beside the machine found out the rest.
In a 2003 interview, as Wikipedia reports it, Endo said he somewhat regretted how hard Druaga turned out to be. He thought it might have made players paranoid about finding the secrets. In 1985 he left Namco and started his own company, Game Studio. The notebooks, and the habit of sharing what you found, had already begun to spread beyond that one cabinet.
He hid one tower and called it a bug, then built sixty floors that could only be solved by asking someone else. What have you not found yet, that the person standing next to you already knows?