EDIT: I forgot to mention, if you wanted to add a point, you can ctrl/Command click on the line. That will add an extra editable point!

Also, TKTKTK informed me that on some versions of Sai, the Linework layer may be called a vector layer.

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Just wanted to post an example of how Sai makes using a mouse easier. I use a mouse a lot instead of my tablet, But usually only use it on MS PAINT with the linetool or GIMP/Photoshop with that point selection tool... I was surprised that the lineart tool on SAI would have better control- Even enough to simulate Pen pressure!

How to use Pen Pressure with a Mouse in Paint tool Sai

1. In the layers window, select the paper that has a pen icon on it. This will create a linework layer.

2. Select the pen brush. Now you can draw a basic shape. It may be shakey, but doesn't worry. You can fix that!

3. By hovering the cursor over the line and holding down a button on your keyboard, you can edit the lineart.

You can hold down Ctrl or Command keyto move the points. Alternatively, you can use the edit brush in the toolbox.

If you used a mouse, those shakey lines could mean excessive points which can be a pain to move around. It might also slow your computer down by having too many points.

You can use the eraser brush to delete lines. However, if you want to be more precise, you can hold down the Alt key on your keyboad. By holding this and clicking a line, you can delete a line between two points.
By clicking a point, you will delete the point and the line will change shape.

4. In order to do pen pressure, you can click the Pressure brush in toolbox. This way, you can click, hold and change any point.

By dragging the point to the right, the line will become thinner.
By dragging the point to the left, the line will become thicker.

Ofcourse, you can also use these tolls when you are writing or using a tablet. They allow more control than a tablet, in my opinion and are also helpful if you want to work on a laptop on the guy when a tablet might be a hassle to bring.

The only thing I don't like about this tool is that it doesn't allow for varying opacity. That would make it perfect, in my opinion.