Qrow and Summer were once part of Team STRQ, along with Taiyang and Raven. Qrow briefly mentioned in volume 3 that him and Summer got along well. He also mentions that her and Taiyang were the ones that pulled off the prank in getting him to wear a skirt during the initiation ceremony at Beacon. Despite Raven being Qrow's sister, Qrow still maintained a close relationship with Summer and her family, leading to her daughter Ruby calling him uncle. After Summer never came back from her mission, Qrow was the one who told Taiyang that she wasn't coming back.
This news greatly devastated Qrow and this is also when he beacme an alcoholic. After Summer's death Qrow became very close with her daughter Ruby and Ruby in turn returned his affections. In volume 3 chapter 7, Qrow shows Yang and Ruby a picture of team STRQ with him and Summer standing near each other. He then proudly proclaims that they "looked good". In the last episode of volume 3 Qrow eventually told Ruby about her and Summer's silver eyes and the legends behind them.
In volume 7, chapter 4 Qrow tells Ruby that her mom, Summer would be proud of her. Ruby then asks him more questions about her mother and they further discuss Summer. Ruby then asks Qrow what Summer would have done about Salem after learning the truth about her. Qrow then responds that he thinks Summer would have probably pressed on anyways. He then tells Ruby that "Summer was always the best of us, a bit of a brat though, but hey he likes brats".
Ever since Qrow was introduced in volume 3, hummingbird became a semi-popular ship in the fandom, since Qrow resembled Ruby greatly, even more than he resembled his biological niece. People were also suspicious how Ruby admired him so much to the point where she modeled her weapon after him. Even though the creators have confirmed that Ruby is not Qrow's daughter some fans remain skeptical. Then there are some fans who think that Summer and Qrow simply had a similar relationship to Lily and Snape from the Harry Potter series. Some people also believe that Qrow simply had unrequited feelings of love for Summer and he never told anyone about his feelings, not even Summer herself. Fans have also theorized that Qrow might reveal more about Summer in volume 9 of Rwby.
- "Hummingbird" comes from the fact that Qrow is named after a bird and hummingbirds are birds. Also hummingbirds are most active in the summer time.