In any Harvest Moon game that has a Courtship and Marriage option, there usually is one Eligible Girl or Bachelor whose courtship is more difficult or complex than the others. For example, in Harvest Moon Cute DS, that bachelor is Skye, whose initial encounter is a 'secret' that must be uncovered before you will meet him regularly in the Valley. In 'Island of Happiness', many of the Eligible Girls/Bachelors must be unlocked, making it the most complex and challenging of all Harvest Moon games perhaps where Courtship and Mariage are concerned.
Princess Debut, although it does not include farming, which is the backbone of any Harvest Moon game, resembles Harvest Moon in its Courtship aspect. There is one bachelor in the person of Kiefer whom you will not be able to meet until you have completed the game once, making him essentially a 'secret' option. Courtship of Kiefer once you have met him, however, is fairly straightforward. It is Luciano, a bachelor who is available almost from the start of your first game who represents the true challenge in Princess Debut.
It is not difficult to persuade him to become your partner. You can do this as early as the 6th day AFTER the first Dance Competition. The challenge arises long afterwards, as Luciano will leave to participate in a World Dance Competition. In some circumstances, he will leave of his own volition. In others, he will receive a letter from his King, commanding him to participate in the Competition. If you have made him your Partner prior to his departure, you will be left without a partner either on the 19th or 20th day of your sojourn in the Flower Kingdom.
It is apparent, not only from my own experience but from the experience of a number of other players as well, that Luciano's possible return on the 29th Day of the game is a rare occurrence that requires a specific set of circumstances that most players fail to create.
There are Princes who provide you with many opportunities to ask for or accept a partnership with them. Liam, Vince and Cesar are readily available at many different points in the game.
There are others, such as Klaus and Kiefer whose Affection may increase to 100% fairly early but whose Events rarely offer any opportunity for partnership. In fact, I believe there may be only one opportunity to become Klaus' partner. I have not explored options with Kiefer sufficiently to discover if there are more than two opportunities to make him your partner but I believe that your first oppportunity can occur as early as the 20th Day provided you go to the Dance Hall then to practice by yourself. I was not able to trigger this event on the 19th, which makes me think that the 20th is the earliest opportunity. The second occurs when he comes to your room to introduce you to Foxtrot Forest. The default opportunity for this is the 23rd Day, actually entitled 'Secret Lesson' but as I obtained the first event at the Dance Hall days earlier, I obtained the second event days earlier as well.
In fact, it appears that, after the initial visit to Foxtrot Forest, you will have the option to practice there with Kiefer every day. If you dance only once with him on any given day, you won't be given an opportunity on that day to ask him to be your partner. If you continue to practice, however, you will be given another opportunity to ask him, encouraged by Kip. To avoid asking the partnership question, simply choose the option to continue dancing with him instead.
This being the case, it is only with respect to Klaus that you are given no more than ONE opportunity to become his partner. (There was a psychological aspect to the endless pursuit of Klaus by the two other Princesses that caused me to look less favourably upon him in my first game than I otherwise would. It is not his fault, after all, that he is being stalked by the two girls. In fact, partnership with Klaus is very romantic in its way, especially in view of the fact that he has been searching for your counterpart since childhood. I did feel a little guilty accepting his love, knowing that I was not the REAL Princess. Her own warning at the start of the game with respect to the Emerald Necklace makes it clear that he never forgot him either!)
Luciano actually is a Prince whose events offer quite a few opportunities to become his partner before his departure. The challenge with respect to Luciano is not to make him your partner but rather to ensure his return on the 29th Day. Sad to say, 100% Affection and excellent dance scores appear to have nothing whatsoever to do with his decision. The real opportunity to set him up as your Partner for the actual Ball occurs on the 19th Day. You must ask him to become your Partner after you dance with him at the Practice Hall. He will not accept but then will ask you to meet him the next morning, as he needs to explain something to you.
When you meet him on the 20th Day, he will take you for a walk at Rumba Beach. Here, he will explain that he intends to participate in the World Dance Competition. I am not certain if your responses actually matter at this point. No matter what you respond, you will tell him that you will wait for him, eliciting a promise from him that you will be 'the first to know' what occurs at the World Dance Competition.
Oddly enough, you can experience this Event even if you have a partner if, during the Event at the Practice Hall on the 19th Day, you ask him to be your partner. Any other response at that point will result in an announcement there and then that he is returning to his Kingdom to enter the World Dance Competition and a rather terse statement that he was glad to have one chance to dance with you before his departure.
I therefore am inclined to believe that it is the Event on the 19th Day and the response you make THEN that is critical to his return. This leads me to suspect that you indeed cannot make Luciano your partner before the World Dance Competition as, if he is your partner, you will not experience the Event on the 19th at the Practice Hall. Instead, you will dance with him on Foundation Day and after winning the competition, he will receive the command from his King to return to his own Kingdom to enter the World Dance Competition.
There may be one other situation that allows you to be his partner before he leaves that yet will allow him to return at the 11th hour. I will reserve final judgement on this until I manage to experience it.
I actually have completed most of a Walkthrough for Princess Debut at this point, having initially decided NOT to cover this game in a guide. There are enough variations in the game to merit a little Walkthrough and in fact, the difficulties with respect to Luciano would be sufficient to make me believe that a Walkthrough will help other players!
At present, I am going through the game with Klaus and Kiefer as my partners and in the third file, working through the game after the 20th without a partner to experience Luciano's return. Even with Klaus as my partner, I experienced the Event with Luciano at the beach when I rather shockingly asked Luciano impulsively to become my partner on the 19th. As in the file where I remained single, Luciano then promised at the beach that I would be the first to know the results of the World Dance Competition. I will be interested to see if anything further occurs in this file with respect to Luciano... I doubt it will make any difference to my relationship with Klaus as he appears to be oblivious of the event. In fact, I experienced a very amusing Event with him at the Beach later that day involving the two awful Princesses who have been stalking him since the start of the game.
Finally, I'd like to make a comment about any attempt to write a guide for any complex game before the game has been played exhaustively for a year or two. The very first Guide I ever wrote was written for 'Friends of Mineral Town' long after the game actually was released. I had played the game numerous times, making errors and then correcting them in subsequent games.
As I began to write Guides for other games, the time span between the game's release and the publication of the guide grew ever shorter until, with some games, I actually was given an opportunity to play the games BEFORE their official release in order to be able to make a guide available on the internet to players at the time of its release.
I do the best I can to cover the game adequately as quickly as possible but it still takes time and much experience with a game to discover all the little variables that can affect results. Although I moved on to 'Rune Factory 2' after writing guides for 'Island of Happiness' late in 2008, my guides for 'Island of Happiness' are NOT completed. Natsume blessed us with a veritable cornucopia of Harvest Moon games last year, not to mention 'Princess Debut'...
Very often, I will receive emails from players making reference to a statement in a guide that has not be updated or corrected because I haven't had the time to do it. In other cases, players actually DO send me new information but for the most part, I am frustrated by the inability to edit and update my guides as quickly as I would like.
In other words, even when I do complete an initial Walkthrough for Princess Debut, I shan't expect it to represent the totality of possibilities with respect to the game.