Alternative Character Interpretation: Some readers have noted that Rin developing intense feelings for her adoptive father basically out of nowhere to the point of cutting out all other possible love interests (and him just going with it) might be the sign of something darker going on.
Audience-Alienating Ending: The manga's ending is rather infamous among anime and manga fans, mostly due to becoming a Wife Husbandry story at a very late stage. While Values Dissonance may have made it slightly more palatable in Japan, plenty of Japanese readers hated it too. This is reflected in how neither the TV anime adaptation nor the live-action movie adaptation cover anything after the manga's Time Skip. It's to a point that the term "Usagi Dropped" was born to refer and warn people in case another series ended the same way as Bunny Drop did.
Fanon Discontinuity: A good chunk of fans insist that the post-timeskip half of the manga never happened. Apparently, the makers of the anime adaptation themselves agreed, since said adaptation didn't even touch that material. A live-action movie similarly did not touch any of the post-timeskip material.
Daikichi/Yukari. The anime, which cuts away the second half of the series, plays this up, in part because almost nobody liked Daikichi/Rin.
Kouki/Rin is a popular Toy Ship. Helped because even if they did become step-siblings, it wouldn't be at an age where it would be awkward.
Hollywood Homely: Daikichi. There are several references in the manga and anime to him not only to his shy and awkward demeanour around women but also to how he's physically unattractive, but the art doesn't reflect that.
It Was His Sled: Rin and Daikichi ending up together has been cited as one of the most poorly hidden manga ending spoilers out there. It's not uncommon for the series to basically be referred to as "That manga where a man raises a little girl then ends up dating her 10 years later".
Memetic Mutation: "Usagi Dropped".Explanation The twist towards the end of the manga where Daikichi ends up with the woman he's raised since she was six is infamous amongst manga readers. As a result, the term "Usagi Dropped" pops up whenever themes of Wife Husbandry appear in other media.
No Yay: Rin and Daikichi after the 10-year time skip. The idea of it caused revulsion for many readers.
The timeskip could have been a good way to show a single father's challenges with raising a pubescent daughter, along with expanding on Rin's bond with Daikichi at a more mature level.
Some feel that a teenage girl developing feelings for her adoptive father and how both of them deal with it might actually have been quite an interesting plot if it was handled... differently.
When Haruko runs away, the end of the episode/chapter has her deciding to just bear her unhappy marriage and relationship with her inlaws. She is not encouraged to fight for her own happiness despite the obstacles as the message of an American show might be. Deconstructed after the Time Skip, when Reina casually mentions that her parents separated at some point, suggesting that it wasn't the right path for Haruko.
On a related note, the scene when Daikichi's sister expresses concern about her fiance's desire to start a family immediately runs into some minor Values Dissonance. Daikichi does give her good advice (of the "talk to your husband, it's no use talking to me!" variety), but largely dismisses her concerns, deciding that the "leisure activities" his sister wants to keep are expendable — you have plenty of time to yourself at work, right? While very upbeat on one level, suggesting that spending all of your time at work or with your children is not automatically a huge sacrifice, a more Western audience would probably take her concerns more seriously and agree that someone who wanted to keep a free-wheeling lifestyle isn't yet cut out for motherhood — and it's unfair for her fiance to expect her to get pregnant, give birth, rearrange her lifestyle and cope. Of course, the fact that she's a bit of a Jerkass loses her sympathy points.
It's perfectly acceptable for Rin and Kouki, who are both six years old, to walk to and from school alone. Depending on where you're from, letting a child that young venture out alone isn't socially acceptable and is considered dangerous, while in Japan it's quite common and the norm. It does help that the two of them are taught about Stranger Danger and told what to do if they're approached by someone they don't know.
