My Next Life as a Villainess: All Routes Lead to Doom! has lots of dreamy guys to choose from, but Keith Claes stands out from the rest as the best option. Keith is one of the conquerable love interests for the heroine in the fictional game Fortune Lover, in which the anime's story takes place. In the original version of the game, Maria Campbell wins his heart and turns him from an emotionally damaged playboy into a faithful suitor who would do anything to protect the woman he loves... which includes killing or banishing his evil and abusive adopted sister, Katarina Claes.
But in the new timeline, the quirky and kind version of Katarina is the one everyone wants to be in a relationship with -- especially Keith. After she refused to let him lock himself away so he could spend years stewing in his misery and loneliness, she instead forced him to accept her love and attention -- becoming the most important person in his life. Now, he spends every day by her side, fiercely trying to keep the rivals for her affection at bay so that no one else can win her heart before he does.
The fact that Keith has grown up with Katarina under the same roof means that he knows her the best out of all her suitors, so he has an advantage when it comes to knowing what she wants and what she likes. But it's the way that Keith treats Katarina that makes him the best option as a love interest. He is always there when she needs him, providing kind and helpful support. When she spent the summer playing and spending time with her friends instead of completing her homework assignments, he stayed up all night to help her finish. He accompanies her everywhere to watch over her and make sure she is safe. When she is alone with Prince Geordo, her fiancé who is prone to making inappropriate advances, Keith shows up to stand in the way and protect her honor. Of course, his motives are selfish, but it is still a noble thing to do.
Keith also has the most opportunity to make a move, too, because sharing the same house as Katerina means that he is expected to be with her almost all the time. But beyond that, his careful attention to detail and his striking good looks also go a long way towards making him her ideal boyfriend. If anyone deserves to become the hero of her story, it is definitely Keith Claes. Unfortunately, at this stage in the series, it is obvious to everyone except Katarina just how much he loves her.