What pen does Ou Kai use to write without edges and corners?

Round pen. European-style regular script works are written with a round pen. The strokes are round, without edges and corners, and the style is very peaceful, so Ou Kai, who has no edges and corners, writes with a round pen. Ou Kai is a regular script font created by Ou Yangxun, a great calligrapher in the Tang Dynasty. It is characterized by the combination of harmony, strong stippling and cohesive brushwork.