Marriage, or the benefits of marriage, is the main goal for the plot of each drama; granted, it's approached by the leads in different ways. Both dramas also contain quirky humor, fantastic supporting characters (and family members), and a sweetly developed romance (though frustrating at times).
These two slice-of-life dramas take place in extraordinary situations, and have a similar tone in both the comedy, romance, and character growth. Both dramas' female and male leads are similar in how the female lead seeks her place in the world (particularly through a job) and the male lead often keeps to himself but opens up over time. Hoshino Gen (Hiramasa Tsuzaki in Nigeru) also sings the theme song for both shows, a similarity that coincides with the overall vibe of the shows.
They're both slice-of-life in a way, but contain quirky humor and relationships that go from passive love/hate to the characters being on the verge of marriage. The main characters also tend to go outside of their comfort zone in order to grow as people or accomplish tasks.