Aki

Aki is an amazing single target damage dealer unit that shines with investment, both in ascension and artifact. Her biggest claim to fame is her ability to replenish her mana after killing a target with her main skill and ultimate, allowing her to basically main>ultimate>main if everything crits. That being said, she really wants her artifact to be at least leg+, since the added speed makes it much easier to get her rolling, especially if the rest of your team isn't as invested and is basically acting as a meat shield. Considering she still gets mana refresh on her main skill, she doesn't necessarily need to use her ultimate to be effective, making her work very well with units that need to ult a lot (Hong) and hyper buffers like Jiho. You can, for example, run both Linzy and Aki in the same team and use Jiho ultimate to deal huge amounts of damage to bosses. The addition of origin keepsakes make it easier to get more crit rate/damage on her, but you should still focus on pairing her up with units that can buff her crit rate - Jiho again comes to mind. It doesn't hurt to mention again how much she needs to get her artifact to at least leg+ to really start snowballing. Another huge benefit to Aki is how easy she is for new players to acquire. Since the addition of the choice banner, anyone just starting the game can choose Aki as the focus unit to get her ascended right from the get-go, which is a huge boon to a new account for pushing content. Aki has been a top tier dps since her release, being able to work as a main dps in all guild raids but Rudra so far. She's also extremely helpful in raid events, helping players push for a high score to maximise their currency income. In PvP, Aki is a huge threat and can easily snowball matches, especially since she works well even without her ult.