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.