From Keen On Keys.

The Rapman is a small keyboard with 32 mini keys, 25 tones, 30 rap patterns, scratch disk, microphone and voice effector. Released in 1991, it is the world’s first keyboard designed just for rap.

Support this channel and buy a song or album on Bandcamp: https://keenonkeys.bandcamp.com

0:00 Intro
0:21 Overview
2:29 Hip Hop
6:10 Other Models
7:14 A Look Inside
10:17 Tones
13:26 Scratch Disk
14:28 Patterns
22:44 Microphone
23:30 Voice Effector
24:45 Feedback
29:12 Connecting Other Instruments
31:42 Conclusion
34:19 Outro

Listen to some tracks on Soundcloud:

Magazine scans taken from muzines:
http://www.muzines.co.uk/articles/casio-rapman/884