Neo Nectaris

From Base Nectaris Legacy page:

Neo Nectaris released in Japan for PC Engine + CD / DUO (Super CD-Rom). Developed & published by Hudson Soft (HCD4062).

Distinguishing features of this title include: a fantastic soundtrack (in fact, this is the only title in the entire series that doesn't simply rehash tunes from the original game); eight new weapons that are exclusive to this release; the inclusion of five maps designed exclusively for 2-player matches; Martian as well as Lunar battlefields; 48 new maps (exclusive to this title) + 32 maps from original campaign.

Note: you do not play the original campaign maps in the updated Neo Nectaris environment. When playing the original campaign, it's as if you own the actual Japanese HuCard, since Hudson simply put the Nectaris ROM on the Neo Nectaris disc. The same technique of putting HuCard ROMs on a CD-ROM can be found on the "4-in-1" SCD that was a software pack-in for the TurboDuo (the North American version of the Japanese DUO console). NEC's DUO was a consolidation of a PC-Engine + CD-ROM + upgraded RAM into one console.

For more information, be sure to check out the Neo Nectaris FAQ (archived).