@LilG, the rom and the CHD are available on planetemu.net , just use its search tool, type Tetris Dekaris and you'll find two results. You just need the bigger file: (Tetris Giant / Tetris Dekaris (MDA-C0076)
I'm using Demul 0.7.
Select plugins, configure, and go to Run Naomi/Naomi2 and select it from the list.
By the way, you also need the naomi bios and the segasp rom.

That looks cool where did you get the game from?