Tengai Makyou II: Manjimaru

Tengai Makyou II is one of the all-time best RPGs, period. It has been remade for the GameCube, PlayStation 2, and Nintendo DS, and had an equally awesome spinoff starring Kabuki.

It's like the Mother series in many aspects, including its mostly-Japan-only status.

Character Viewer
At the PC Engine CD boot screen, press Run and as the words "Just a moment" appear on the screen, quickly hold Run + Select. You can cycle through the different NPC graphics by pressing Button II.

Leftover Sound Data
The disk has some leftover tracks from other games, like Ys 4, and can be listened to with a ripping utility.