Throughout all of Death Note, Light Yagami thought he was untouchable. He gained the killer notebook and used it to try and create Kira's new world, even slaughtering Raye Penber and the FBI agents who pursued him. Then Misa joined his side, and together, they took on L. Then Light found himself backed into a corner. The only way out was a proxy -- and he needed one ASAP.
That proxy would turn out to be Kyosuke Higuchi, a businessman working for the Yotsuba corporation. Light had no idea who Higuchi was, but that didn't matter. He just needed a third Kira to keep L busy and hang onto the Death Note and, when the time was right, Light would turn on Higuchi and reclaim what was his. Higuchi never saw it coming.
Rem Finds Kira Number Three
Misa Amane got herself captured by L because the Japanese police found enough forensic evidence to fairly suspect her of being the second Kira. Misa was put into confinement and it was only a matter of time until she cracked. Rem marched right up to Light and demanded a solution, and sure enough, he had one. It was time for Kira #3 to be born, and Light buried Misa's notebook in a forest and handed his own to Rem in secret. It was up to Rem to fly off and find a human who would use that notebook for personal gain, and thus become L's new target when the time was right. Light didn't know how long this would take, but he had no choice. Rem flew off, and in the coming weeks, she scouted the area and decided on a new Death Note bearer: Kyosuke Higuchi.
About three weeks into Light's own confinement, Higuchi had the Death Note and was starting to use it to kill off business rivals, immediately drawing L's attention. Higuchi reveled in his grim new power with Rem at his side, and try as he might keep a low profile, Higuchi drew attention to himself. L used a trick to "confirm" Light and Misa's innocence as Kira, and the three of them went after this new Kira together. They didn't have official police support and Light and Misa had lost their memories, but even so, Higuchi's days were numbered. He was a temporary solution, not the true new Kira.
Kyosuke Higuchi's Council of Kiras
Until Higuchi got himself captured at the hands of L, he had a comfortable little kingdom set up for himself. He enlisted the aid of seven other ambitious members of the company and urged them to form a secret team with him, meeting every Friday after hours. Higuchi blended right in with the other seven members of the team, and everyone there knew that one of them was Kira, but not which. With this setup, Higuchi could provide team input without intimidating anyone too much, and he and the others could reason out who to kill, how to kill them, and when. Carefully, the eight-man team chose high-ranking members of rival companies and killed them, and as Higuchi hoped, Yotsuba stock kept rising at the expense of its rivals. Higuchi was getting richer than ever, but only that: rich. He wasn't trying to create his ideal world, nor was he fully prepared for the true extent of L's investigative abilities. L sent Aiber and Wedy after him, and Higuchi had no idea.
This was all going according to Light's plan. Higuchi was powerful enough to warrant L's full attention but wasn't sly enough to escape capture. So, a memory-less Light helped L capture him, and Soichiro Yagami claimed Higuchi's notebook from his car. That gave L and Light a chance to handle it too, and Light got all his memories back. He killed Higuchi at once by using a hidden scrap of notebook paper in his watch, then gained official ownership of the notebook again. Higuchi thought he had it all: money, power, a killer ability, and a girlfriend in Misa Misa.
But Higuchi was operating on borrowed time, and he was just a convenient hiding spot for Light's notebook until the time was right. Being Kira is more than good business; it's a dream. And Higuchi, in the grand scheme of things, dreamed small.