HATSUNE MIKU: COLORFUL STAGE!

In-game achievements and rewards rely on adding friends and playing together with them - many of these are impossible to complete if you prefer to play alone or don't have any friends to add in the game.

There's a new event basically every week, with boosted rates for featured characters and special event bonuses and prizes. Something is always happening, and if you miss out now it'll be much harder to get the featured characters/cards again in the future.

Rhythm game - there's a plot, but there doesn't seem to be a "win state" or ending. Constantly updating with new weekly gacha events.

There is an optional subscription service for in-game rewards and advantages, which is cheap on the surface but could add up especially if the player forgets about the game and never cancels it. The cheap monthly payment means it's easy to ignore a tiny bit taken out of your bank account every month, and it's easy to forget to cancel it if you stop playing.

When playing single-player, your score is determined almost entirely by whatever team you have at the time. As long as you pass the level, you will ALWAYS get a "C" until you have a rare enough, high-level enough team, no matter how good your performance is. Unless you play on co-op mode, the only way around this is to get better character cards and upgrade them with in-game currency and active effort. Your actual skill level matters pretty minimally.

Spending money on premium currency means you can use the gacha more. More gacha pulls means a higher chance of getting rare, high-quality cards, and any lower quality or duplicates you get will still give you in-game advantages. F2P players can use the gacha, but after the first few days of playing it becomes MUCH harder to do. Paid players can get new, better stuff whenever they want.

If you fail a level, you can pay a small amount of premium currency to continue anyway. You can see your friends' successes in terms of player rank, featured characters, new titles, etc. which mark their progress in the game ahead of you without giving any insight into how good or bad they actually are at the rhythm game itself.

There's a billion and one achievements and character rank-up tasks, and you're flooded with rewards from them in the beginning before they drop off into almost nothing a few days into playing the game.

Having rare cards, especially ones that have been upgraded and leveled up a lot, means that it's hard to imagine abandoning all of the luck and hard work that got you to that point

Beginner's Login Campaign, regular player login bonuses, limited time monthly/seasonal login campaigns; campaigns often run concurrently or overlapping so you're always working towards one login streak or another.