This paper presents LyriSys, a novel lyric-writing support system. Previous systems for lyric writing can fully automatically only generate a single line of lyrics that satisfies given constraints on accent and syllable patterns or an entire lyric. In contrast to such systems, LyriSys allows users to create and revise their work incrementally in a trial-And-error manner. Through fine-grained interactions with the system, the user can create the specifications of the musical structure and the story of the lyrics in terms of the verse-bridge-chorus structure, the number of lines, words and syllables, and most importantly, the transition over semantic topics such as hscenei, hdarki and hsweet lovei. This paper provides an overview of the design of the system and its user interface and describes how the writing process is guided by a state-of-The-Art probabilistic generative topic model that is trained without supervision. The system works for both Japanese and English.