Ten Key Pad
From Sega Retro
The Ten Key Pad (テンキーパッド) is an accessory for the Sega Mega Drive. It was built for use in conjunction with the Sega Mega Modem, and aids in navigating menus. It also allows the user to input codes found on modem-compatible game cartridges. It is known to be compatible with Nikkan Sports Pro Yakyuu VAN (Baseball info service) and the Sega Mega Anser.
Like the Mega Modem itself, the Ten Key Pad is a very rare accessory and never saw a release outside of Japan.