This study proposes a method for creating dynamically deformable Gothic ornaments and an interactive design support system that utilizes this method. This project specifically focuses on tracery found in window frame decorations in Gothic architecture. Traditionally, motifs of Gothic tracery are designed with combinations of arcs. However, parametrically controlling these arcs to achieve continuous deformation is challenging due to the potential for significant changes in their conditions. Therefore, this study attempts to approximate the shape of motifs using metaballs, a modeling algorithm in computer generated imagery (CGI). Metaballs allow for the creation of organic-looking surfaces or curves by arranging multiple density distributions and visualizing their iso-surface. By attenuating the density value in certain areas of each metaball, it was confirmed that some motifs commonly seen in the Gothic style could be approximated. This technique also makes it possible to animate the gradual transformation of motifs by changing the attenuation rate. Applying this technique, an interactive design support tool for Gothic ornaments was developed.