Goddess of Victory NIKKE fits what you are asking.

It is a high quality Free-to-Play mobile game played in portrait mode and completely playable with one hand (depending on how wide your device is). As long as your don’t care about leaderboards, it also isn’t Pay-to-Win. It is playable on PC as well, which is how I play these days. As a Day 1 Player, you don’t need to spend any money to play, enjoy, or progress in the game.

In terms of negatives:

• Some people may not like the anime art style (game is playable in various language dubs, including Korean, Japanese, English, and depending on region, Chinese, which are optional downloads to reduce filesize) or the character designs, which have huge… personalities

• If you don’t care about time limited events or being at the top of leaderboards, its not hostile to your playtime and mental health. Go at your own pace.

• It is a gacha game for characters and skins, but the game gives players a lot of options, so unless you’re trying to be #1 on the leaderboards in your server, having every character max level isn’t that important.

They recently added a “Story Mode” for the campaign, which significantly reduces the difficulty of all the missions in the 40+ campaign chapters so that players can enjoy the story without needing to have as powerful characters. I think you get reduced rewards as well, but its a nice addition. You can also get photo film rolls to unlock past time limited events (not licensed or collab ones though) so you can enjoy the stories of those as well. You don’t get the rewards for them as they were running, but still can experience the stories and minigames. You get plenty of free currency for free character rolls, no money is needed. Unless you really want a skin or really like a licensed collab and want to buy an IP specific bundle or something.

Basically, for a free player, there is A LOT of story content available to keep your busy for a while. Play at your own pace, and don’t worry about leaderboards and you’ll be mostly fine. The biggest advice is to try to get 5 characters 4 times each. If you are playing the regular difficulty story, there is a point where it is required to progress, and is often referred to as the only “wall of progression” in the game.