Beating the demo gets you extra items for the game.

Matryoska	How to unlock
Matryoshka AT	Load saved demo file.
Matryoshka DF	Load saved demo file.
Matryoshka LC	Load saved demo file.
Matryoshka MA	Load saved demo file.
Matryoshka MD	Load saved demo file.
Matryoshka SP	Load saved demo file.
Matryoshka TC	Load saved demo file.