My next project was a quick one but looks like a fun game. It's called Holy Diver. The story is that Irem was going to bring it to the US but it didn't make it. The game reminds me of Castlevania. It's a shame it did not come out in the US. The game used a custom board by Irem that seemed to use common logic chips to accomplish 128Kb PRG-ROM, 128Kb CHR-ROM, and Mirroring changes. Pretty nice. It's similar in capability to the Nintendo MMC-1, and I believe if the game had come to the US they would have used that. And so that is what I used.

For a reproduction you will need a SKROM or SLROM board. The primary concern is that the board supports the 128K/128K chips. SKROM has extra WRAM but it is not needed. I recommend giving this game a try.