Let’s say this is out of the thieves universe. :)
who holds the umbrella when it rains
They trade, though usually it’s Mikasa because Annie hates having to walk with her arm extended as much as it has to be to cover Mikasa.
who is the grumpiest in the morning
This is a toss-up. Annie hates getting out of bed, but she’s reasonably decent once she’s actually up. Mikasa, however, will make several threats if she doesn’t get to go on her morning runs. (She is very grumpy when she’s released from the hospital after getting shot, since bedrest means no running dammit.)
who worries more when the other is sick/hurt
HOLY SHIT ANNIE LEONHARDT IN THIEVES WILL CODDLE HER SICK OR INJURED GIRLFRIEND TO THE MOST INTENSE DEGREE ANYONE HAS EVER SEEN. CHRISTA WAS VERY STARTLED WHEN SHE GOT A BAD COLD BECAUSE ANNIE WAS SO ANXIOUS ABOUT TAKING CARE OF HER.
ANNIE NEARLY LOST HER FUCKING MIND AFTER MIKASA WAS SHOT BECAUSE SHE COULDN’T STOP WORRYING EVEN WHEN THE SURGERY WAS OVER AND MIKASA WAS OKAY.
who plays pranks on the other
They tag team playing pranks on Eren and Ymir in a rotation. They are much loathed for their partnership.
who is always the first to suggest cuddling on the sofa
Annie Leonhardt is a cranky koala.
who insists on creating nicknames for the other
They’re not really a nickname couple in any universe but the Crimson Tiger universe. (There it’s Mikasa.)
who drools on the other when they’re asleep
Mikasa refuses to admit this, but Annie has caught her drooling if Mikasa’s face-planted on her chest or back, or in her lap. Mikasa also refuses to believe it until Annie shows her a picture of it.
who says ‘I love you’ first
right after gettin’ shot