My Lovey-Dovey Wife Is a Stone Cold Killer Vol. 4 (manga)

Not even a top-notch assassin is safe from the common cold! When a new neighbour in the apartment complex masquerades as Setsuna's new boss, suddenly the notable killer is engaged in a different pursuit: babysitting. It takes all of Setsuna's skills to watch out for her new tiny tyrant, only to succumb to the flu! While nursing a sick assassin back to health, the married couple dream over the kind of home they'll build in the future.