SAI format is generally only used in Paint Tool SAI, so if you hope to turn any other graphics, for example Adobe Photoshop large files (.psb), you have to use the original program. As far as we know, this is the only way how to achieve this conversion.
Convert Adobe Photoshop Large Document Format to Paint Tool SAI drawing.
We found one software available in the database for this conversion.
Microsoft Windows software - convert psb to sai on Windows
A painting software
Convert from psb file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.