In Sigma Harmonics, gameplay is broken up into roughly five segments. Chronologically speaking, the sequences of gameplay are: "toki tsumugi," "tamashii no kage/toki no saien," "kokuon," "chou-suiri," and "battle." Below are some cursory information on all of these, with the Japanese script and attached translations.
"Toki tsumugi" is used by Sigma and Neon when the two characters are in the Hall of the Great Clock. Within this room, they begin the time spin ritual in order to traverse the different times of the game, and find clues to many mysterious events that occur throughout. Once the ritual has begun, the screen changes to the card gameplay, in which Neon's collected cards take the player to different moments of an incident.
During your time with the game, you'll find many instances of a black monolith standing in your path. This signifies that some event happened in that location in the past, and is dubbed the "Shadow of the Souls." When a player finds these, he can re-enact what circumstances unfolded, and in another words, have a "recapitulation of the time." Also, the monolith appearing depends on the time during the game, so it is suggested that you adventure in many areas to chance upon one.
A Moment of Sound
These so-called "moments of sound" are visualized by what could be called medals. Essentially, they are items collected throughout the story that give clues to the many different mysteries surrounding the narrative. The more you collect these "moments," the better your chance of success in finding the truth become. These "medals" can be sought from conversations with non-playable characters, or even suspicious looking places on the map.
As I previously stated, more medals equal better chance of finding out the truth. This is especially important in the act of inference. By linking different mysteries and connecting the missing dots, so to speak, Sigma either can infer right or wrong. What this means in the long run is that a correct inference will give the player a better chance of winning against battles. And look what we have next?