Walkthrough 

At the very least, you're going to need 2 "master save" to see EVERYthing. 
One is virgin heroine for the virginity loss line in display picture, 
second is slutty heroine with some prostitution and pillow deal stats for H event.

Virgin Heroine answer choice : No idea -> Normal Girl -> Any
Slutty Heroine : Two timing -> serious girl -> Any
For the Virgin Route, keep the heroine virgin until the very end, you can create the master save after you've solved all the riddle.

Phase 1
- 1F East - TV room, get crowbar from the back of drawer.
- 1F Center - Dining room, answer riddle in the wall with くま, obtain bear.
- 1F Dining - Kitchen, open locked wooden box with crowbar, obtain cable
- 1F East - Children room for girl, put bear in the table, obtain cable
- 1F East - Children room for boy, plug 2 cable, obtain key

Phase 2
- 1F East - Manga room, check the bookshelves in the following order
Top left -> Bottom left -> Bottom right -> Top middle. Obtain book
- 1F West - Warehouse, go pass the fake chair, there's hidden chest, obtain book.
- 1F West - Safe Room, top left silver chest, answer with 5127, obtain book.
- 1F West - Library, insert 3 book to bottom right bookshelves, obtain key.

Phase 3
- 2F Center - Wine Room, check the wine in table and trigger event, enter the room again afterward, obtain paper knife then use it on right shelves, obtain Necklace.
- 2F Center - Dress Room, obtain Mysterious Coin in Children Room for Boy, insert it into the 2nd drawer from the left, obtain White Dress.
- 1F East - Check Big Mirror, obtain Key. 

Phase 4
- 1F West - Safe Room, Bottom left wooden chest, answer with うさぎ, obtain Music Score.
- 2F West - Piano Room, Play the Piano, obtain screwdriver.
- 2F West - Left Japanese Room, check top left drawer, obtain Key.

Phase 5
- 1F West - Safe Room, Top right silver chest, answer with みどり, obtain Mold Remover.
- 1F Center - Bathroom, Obtain Towel.
- 2F  West - Middle Japanese Room, Clean the mold in desk, read the text, check the wallscroll, obtain Key
- Underground - Pool, do the event, enter again after you can move. 

Collect the following 7 Items : 
Chair from top right of Pool.
Mug from Kitchen.
Empty Pet Bottle from Kitchen, then fill with water from tap.
Bottle of Lotion from 2F Center Bedroom
Box of Tissue from 2F Center Video Room
Pot from 1F West Warehouse
Pencil from 1F East - Children room for Boy
Place 6 items on the 3F left area, the Computer Room at the north will be opened. 
- 3F Computer Room, check the riddle at the drawer, answer with Pencil, obtain Card Key.
- 1F West - Safe Room, use Key Card at the safe, obtain Winding Screw.
- 2F East - Lounge, Talk to Yuyuna, obtain Password, Done. You've solved all story puzzles.
Create master save 1 here.

There are 2 more puzzles left in the game after this point
1 = The last wooden treasure box in safe room, it open the door right next to it for H event.

The explanation is as follow 
- Collect the following 5 items : 
Cross from Wine Room
Egg from Kitchen
Fountain Pen from Potted Plant in the 2F East Corridor
Foldable Fan from 2F West Middle Japanese Room 
Sandals from the changing room in underground pool.
Those items have letters that you can read in the item menu, they read
ちんちんかもかも if you read them in alfabetical order, input that to the last treasure chest.

2 = The last question about "mystery of the mansion", I put the guide for that in the Ending List guide.

For the H event guide, you can read that in the hint room at 3F. 