Answer
The answer is as follows. 
Katrielle and the Millionaires' Conspiracy walkthrough
Puzzle Location: The Rosenberg Room（左のトランク）
There is an unfinished stained glass window.
It's called 'The Red Mountain', but the most important part - the mountain - is missing.
Can you put the pieces in to complete the picture?
It's important to make sure that the two different types of glass are placed alternately.
Slide the pieces to move them into the frame.
Touch them to rotate.
There are several correct answers.
Rotate the pieces and place them so that there are no gaps in between.
Let's look at one possible solution.
First, place the oblong piece in the bottom-right corner of the frame.
Continuing on from hint two...
Take the oblong piece with a part sticking up to the top-right and place it in the bottom-left corner.
Continuing on from hint three...
Take one of the pieces of the left and rotate it so the single triangle is pointing go the bottom-right.
Then place it right at the top of the frame.
You've almost done it now.
The answer is as follows.