 Kọ itẹsiwaju fun paragirafi yii - Mononobe dije gẹgẹbi ọmọ ẹgbẹ ẹgbẹ Japanese ni 4 × 200 m freestyle relay : nínú ìdíje Òlíńpíìkì Ọdún 2008 ní Beijing. Bi o tilẹ jẹ pe o padanu aaye kọọkan ni 200 m freestyle, o ṣakoso lati gbe ipo kẹta ni awọn idanwo Olimpiiki ni Tokyo 1:49.04 lati gba yiyan lori ẹgbẹ relay. Ni ẹgbẹ pẹlu Hisato Matsumoto, Yoshihiro Okumura, ati Sho Uchida ni ipari, Matsumoto nrin ẹsẹ idẹ lati pa ere-ije naa pẹlu ipin ti 1:48.62, ṣugbọn ẹgbẹ Japanese ni lati yanju fun ipo keje pẹlu 7:10.31. 