In the 80's, he had a relationship with singer-songwriter Sezen Aksu that was both romantic and professional. As a couple they put their signatures to works that broke new ground in Turkish pop music, such as Sen Ağlama (Don't Cry), Git (Go), Sezen Aksu'88 and Sezen Aksu Söylüyor (Sezen Aksu Sings). Sezen's music matured in the 90's, when she co-produced her best selling album to-date Gülümse (Smile) with Onno. The A-1 track from the album called Hadi Bakalım (Come On Now) was a hit in Turkey and Europe, and was published as a single in Germany. It was to be later rediscovered in Europop by singer Loona as Rhythm of the Night. She also began to produce albums for her vocalists, notably producing Aşkın Nur Yengi's debut album Sevgiliye (To a Lover) again with Tunç. She was to repeat her success with artists Erener and Yüksel also.