Straight Ruler tool lets you draw straight lines. It is used in drawing buildings, or effect lines in manga.

Prepare an illustration that needs effect lines.

From ① the Ruler tool, select ② Straight Ruler.

Drag ① and you can set the angle. Drag ② to change the position.

Open ① the Brush window and select ② Dip Pen (Hard).

Draw the effect line.

Finished.