[TikiTech]

Not knowing what and how you plan to use this for limits responses.

We 3d print many adapters for the Denso motors. They work quite well depending on loading. If there is going to be shock loads you would need to use metal and bearings with supports so the transmission doesn't take the abuse.

Depending on output needed you can..

CAD an adapter and have it 3D printed. - Many local teams can help with this, even us if you need.
Take a hex axel and mill it down, cut some groves on either side of the output for an "E" clip. Or drill out the end and tap it for a retaining bolt and washer.

From a quick look at this motor in CAD the opening is .238 which is roughly 15/64th..
Which is one step down from 1/4".

If you take a 1/4" hex shaft it will require very minimal grinding / milling to get it square enough to fit. Then use an adapter to get to the require output size.

Post a little more what you plan to actuate with this motor. 1/2" hex, sprocket, pulley, etc.

We have used Denso motors every year since our rookie year. This might be our first year NOT needing to use one.
We do have lots of experience using these window motors and would love to help you integrate them into your design.

Good luck,

Aloha!