Reibo is a shakuhachi piece found in a large number of variants, each of which was transmitted by the komuso of a particular temple. There is a legend that shakuhachi playing arose from a yearning for the sound of the bell, which was cherished by Buddhist priests of the Fuke Zen sect. Pieces entitled Reibo embody this yeaming.
Source: The International Shakuhachi Society
Here is a practice version of the Hijirikai version, played on a shakuhachi 2.4.