From my last post, we know that Mystic Messenger involves an almost constant attention for at least 11 days (the time it takes for a single playthrough), because of its real-time mechanics, which would make it appear as more of a hardcore game than a casual one. However, following the criteria Jesper Jull describes in his article, “A Casual Revolution,” MM still counts as a casual game.
Casual games have positive valence, or have associations with happy or fun vibes. Dating sims involve romance, which have associations with love, happiness, and comfort. Although certain choices can lead to negative outcomes (or bad ends), overall MM has a positive frame work.

The romance options allow the player to choose which personality works best for them, and makes them happiest.
Casual games are easy to use, either building off conventions from outside the game or using simple mechanics that can be easily taught. MM falls into the first category, as the mechanics involve: text-messaging, email, phone calls, and a chatroom. This applies for the first 5 days, which is when the “visual novelization” mode gets added, complicating things as this doesn’t have a real-life counterpart, but even then, the other, more familiar forms still dominate.
Casual games are easily interrupted, allowing players to play for short bursts. Despite the real-time attention needed for MM, it can still be interrupted. The chatrooms and phone calls feature a pause button, allowing players to take a break. They also only take a few minutes to play, and then have hour breaks in between.
Casual games are difficult to master, but feature little punishment for failure. This is the hardest category to measure in a dating sim. Mastery would involve a complete understanding of every romance route, and both the multiple good and bad endings. In that sense, yes the game is difficult to master, but that comes from how long it takes to go through entirely, not that the game gets more difficult as you play; the types of responses you can give vary little as you progress. Also, failure can be a reward as it unlocks the “bad” ending, which many players purposely seek out.
Casual games are juicy. This works for MM because anytime the player responds with the “correct” response, a heart with pop up on the screen, and the player will receive it as a reward at the end of the chat. The game lets the players know when they’re doing the “right” thing.

The heart appears when a character approves of your comment, which is the game’s juiciness.
So, despite its real-time mechanics that make players constantly check it, Mystic Messenger still fits snugly into Jesper’s definition of a casual game.