Sine Mora's story is that of survival. Antagonist Ronotra Koss is a serial killer bent on committing genocide. He has smuggled military grade AI robots for his purposes and kidnapped a young girl of great importance. A group of time traveling partisans is determined to infiltrate the Syriad: a floating fortress that guards the planet, keeping peace and prosperity alive. It's up to Argus Pytel and his team of skilled pilots to protect the world from utter destruction.
Sine Mora is a side scrolling shoot 'em up game. The player controls an airplane in along two axes while attacking enemies. The gameplay world is rendered in 3D, and at key points an in-game cutscene plays in which the camera and plane move. These are often transitions into another part of the gameplay world, but are also used to give the player a new perspective for things such as boss battles. The plane's primary weapons can be upgraded, and players are equipped with a limited-use, more powerful secondary weapon to eliminate more on-screen enemies at one time. Consecutive kills with the primary weapon will increase the game's score multiplayer, while use of the secondary weapon will reset the multiplier. The player's final score is determined by a number of factors including kills, damage taken, and powerups collected.
As the game is marketed as a bullet hell shooter it features two difficulties: normal and insane. The normal difficulty reduces the on-screen ordnance from enemies, while the insane difficulty is geared towards those who are veterans the the genre. In this difficulty the ordnance on the screen is much higher, forcing a greater difficulty level. In addition, four game modes are included: Story, Arcade, Score Attack, and Boss Training. Story mode is the primary mode of the game and allows the player to see the narrative as the game progresses. On the standard difficulty players are given eight continues, while the Insane difficulty yields only five. Completing levels on the more challenging difficulty unlocks an alternate narrative. Arcade mode removes the narrative cutscenes and limits the player to only three continues. Score Attack mode allows players to replay any stage previously completed with only one life. The objective is to achieve the highest score possible and complete the stage. Players do not progress to the next stage after completion in this mode. Boss Training allows players to practice and/or replay any unlocked boss battles. Continues in this mode are unlimited.