I don't even think it's a surprise hit. Three obvious gacha hits that were hitting this year: Wuthering Waves, Zenless Zone Zero, and Infinity Nikki. Infinity Nikki being a sequel to a series of games that people seem to really like. I've never played any but I plan on seeing whether it's enjoyable. For years I didn't play JRPG games that weren't PS1 JRPGs, didn't play any farming sims at all until I tried Stardew Valley, didn't play any rouguelikes/lites until Hades. Spent like a decade mostly playing shooters, console western RPGs (not much Diablo or first 2 Baldurs Gate), Starcraft, and Madden. I was missing out all those years
This year I started looking into what's happening in the gacha space and there's at least a couple more that should be at least first month hits next year. Azur Promila, Arknights: Endfield, Etheria Restart. Ananta and Neverness to Everness if they release next year