One thing that was mentioned is that Taihei and Kanau met as high schoolers, despite the fact that they went to different schools. It is known (by Chapter 96) that Kanau is the daughter of a company president, and it may be inferred that the Doma family was also well off during Taihei's childhood. Thus, it is plausible that Taihei and Kanau's engagement was already arranged by their respective families, and both of them knew it.
However, tragedy struck during Taihei's final year in high school, when he and his mother may have gotten into an accident, killing his mother and causing Taihei to be hospitalized and lose his memory. To rub salt in the wound, Kanau's family called the engagement off. And once Taihei finally physically recovered, he was thrown out of the house through no fault of his own because of the engagement being called off.
Kanau, though, still had feelings for Taihei, so she decided to take up a role in the company and hired Taihei. In an effort to restore his lost memory of their romances, she even hired his friend Bomber despite his incompetence.
Taihei and Umaru's father, still wanting some sort of alliance with a respectable family, then decided to arrange Umaru's marriage to...the Tachibana family! The end of Chapter 71 shows that Alex, or at least someone whom Alex knows, has been looking for Umaru, and it may be due to this arrangement. But once Umaru learned that she was already arranged to be married (though she didn't know that it's with the Tachibanas), she ran away from home and decided to live with her onii-chan, Taihei.
And this takes us to our current happy-go-lucky situation, with Taihei working hard to make a living, Kanau desperate to get Taihei's attention, Alex content with having found Umaru, and Umaru being wary of Kanau, since she could still remember that Kanau used to be Taihei's fiancee when she was little.
And in the end, once Umaru finds out that it's Alex whom she is actually engaged to, she'll change her mind, get married, and live the rest of her days as a wealth mangaka as described in Chapter 28. Taihei, unfortunately, will marry Ebina-chan (who looks similar to his former fiancee), and Kanau will live out the rest of her days as a lonely spinster.
Kirie does radiate high amounts of Killing Intent, when Umaru is around (but not, because she hates Umaru, but because she loves Umaru and hates her own shyness and inability to approach Umaru and confess her feelings to her), when Umaaru is talking to someone else (jealousy) and is also engaging in unconscious self-levitation. Umaru is able to withstand the Killing Intent due to her chakra-levels being higher, due to frequent exposure or because of her bright aura.
Sylphynford can materialize her aura, probably using this doujutsu of hers.
Taihei can radiate Killing Intent, as well, especially when his slackster sister turns the apartment into a pigsty again.
Given that Christina Kelly has posted photos of Umaru, she most likely will have a major role as a cast member for the dub of Umaru.
- Confirmed, Christina Kelly has been announced to voice Sylphynford Tachibana.
Kirie has social anxiety, but is able to talk with children and develop herself in an artistic way (by becoming a book author). Ebina is awkward and shy because of her country 'dialect', but her natural kindness draws people to her. Sylphynford acts loud and tries to become an extrovert despite we knowing she was really shy in her childhood. Umaru created a dependency on her brother and seemingly does not care about other people, but after making friends, she has started to open up.