It seems that the developer, for some arcane reason, included both a save file and a bunch of settings in the registry to control the game. The H-Scene gallery appears fully controlled by registry settings so below a set of instructions to unlock the gallery:
0. Close the game in case it's currently running.
1. Open a text editor and paste the below content in the text editor. (Use Notepad, and not some rich editor such as Wordpad or Microsoft Word).
Content to Paste:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\SOFTWARE\Muramura\Hospital Seduction]
"CurrentLanguage"=hex:45,4e,00
"FirstDayReached"=dword:00000001
"FirstNightReached"=dword:00000001
"FirstNightIsComplete"=dword:00000001
"SecondDayReached"=dword:00000001
"SecondNightReached"=dword:00000001
"SecondNightIsComplete"=dword:00000001
"ThirdDayReached"=dword:00000001
"ThirdNightReached"=dword:00000001
"ThirdNightIsComplete"=dword:00000001
"FourthDayReached"=dword:00000001
"FourthNightReached"=dword:00000001
"FourthNightIsComplete"=dword:00000001
"FifthDayReached"=dword:00000001
"FifthNightReached"=dword:00000001
"FifthNightIsComplete"=dword:00000001
"TrueEndIsReceive"=dword:00000001
3. Save the file with the name "Hospital Seduction.reg". Make sure the extension is ".Reg" and not ".Reg.Txt"!
4. Open the file just saved. Windows will ask if you wish to add the content of the file to the registry. Confirm you wish to do so.
5. Start the game.
The gallery can now be found under "Extra" -> "H-Scene Gallery" with what appears to be all content unlocked. Note that aside from the unlocks, i also included the registry key to set the game language to English. I presume most people will prefer that over Japanese or English. If need be the language can be changed under "Settings" (Third option in the main menu).