Can't catch the Wind!

They're all roughly the same age (21/21/22, and have a cute June-July-August birthday chain which gives them a 32-day window where they're all the same age). They make a cool Tank-DPS-Support triad. Being fictional, they aren't bound by the mutual jingoisms of IRL China-South Korea-Japan. But that's all secondary. Here's my thoughts on why they might work together personally.

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D.Va and Kiriko canonically eat too much junk food, with D.Va missing sleep to game or mission prep (Kiriko's voice lines show she's pushing herself too hard with the Yokai as well). Anran, though herself an overachiever, places great import on maintaining good physical conditioning (don't skip stretches!) and would thus be a good influence about nutrition and sleep schedules for the two.

Anran and D.Va hold themselves to ridiculously high standards (including believing that they're being counted on more than they are to achieve successes) and struggle to turn off their 'on the job' modes. Kiriko knows that the conflicts they've involved themselves in are long-term things, and that they're all more-often-than-not at a severe disadvantage in terms of manpower/firepower. She and the Yokai do what they can to put a dent in the Hashimoto's operations, but don't take it too hard if things don't always work out. Also, she and the Yokai have a strong sense of community, whereas Anran and D.Va have a tendency to take too much onto themselves and not confide in others when they're struggling. She could help them to open up.

Anran and Kiriko either turn everything into a challenge or take everything as a challenge/insult. Anran uses encouragement and criticism both as excuses to work harder, while Kiriko's interactions with other heroes are very quippy and quickly veer into biting sarcasm. D.Va, on the other hand, takes a much more friendly tone with almost everyone, and enjoys herself more. She also openly indulges in hobbies and pasttimes whereas Kiriko devotes all her energy into the Yokai and Anran is always going for self-improvement (which seems to have become ardent self-reliance only). She could teach the two of them to be a little less serious and more friendly (also, I'm sure she'd love showing off her two girlfriends chilling in the background of her streams).

[Personal Trainer x Community Organiser x Social Butterfly GFs]

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EDIT: Sugar, forgot to think up a ship name. I'll get back to you on that.