The current study investigates the articulation of coronal consonants /d/ and /r/ in Japanese. Using ultrasound, we obtained midsagittal tongue images for /d/ and /r/ in three phonological contexts from one male Japanese speaker. Based on the tongue shapes, time-varying changes were analyzed quantitatively using the Principal Component Analysis (PCA). Results suggest that /d/ and /r/ may differ in terms of tongue retraction and dorsal stabilization, while also supporting previous results showing the effect of the surrounding environment. The study demonstrates that quantitative articulatory analysis combining ultrasound and PCA is a useful approach to the spatio-temporal characteristics of Japanese coronal consonants, with implications for future research.