Now that Geordo has gotten serious, it is now Keith's turn. This arc is known as the "Keith's kidnapping arc" where Keith is detained by his older brother, and Katarina, Geordo, Maria , Sora and Larna will set out to rescue Keith. This arc will end with Keith kissing Katarina and confessing to her. Katarina will also acquire dark magic after rescuing Keith. Other stuff from this arc: Keith's old family, Katarina shortspan attention which made her forget Geordo's confession once Keith disappeared, the appearance of a dark magic user called Sarah, the appearance of Alexander, a teddy bear which will stay with Maria afterwards. And that's about all I remember.
So to me, this arc may not be light-hearted, but will definitely develop Keith's relationship with Katarina.
Regarding where this story is heading, after this arc, there is the Fortune Lover 2 arc which starts with Katarina working at the Ministry of Magic, and will introduce 2 love interests for Maria and a new love interest for Katarina. The plot is all over the place in this arc, so I am not sure where it is heading. To this date, Katarina still does not feel attracted to anyone in her harem, and there were some stuff which had been reused again, but there were also some sweet moments.