In Unwanted Harem shows, the last girl to show or confess her feelings for the lead is the one with the best chance of winning him.
Usually they will look like the least compatible couple in the beginning; she will only warm up to him later in the series.
This law is especially likely to hold if the girl who will be last to confess is a Type A Tsundere.
Note that it's the last confession that wins. This rule and First Girl Wins can hold at the same time, and it is entirely possible that everyone else will notice her love before she can admit it.
Corollary: The girl who states her attraction to the lead from the get-go stands next-to-no chance of winning the guy.
The reason for this is simple. The girl in question is the one whom the protagonist will love back after the confession, the other half of the Official Couple. Once the official couple is truly official, the premise for the Unwanted Harem show is gone. Thus, her confession will be the last for the same reason people always find lost items in the last place they look: after that, there's no longer any need to look.
Be warned before you proceed: "Winning", in this sense, tends to be spoileriffic. Therefore, all spoilers in this trope will be unmarked.
- Ai Kora has Sakurako announce her love last. In fact, she doesn't confess until a little over halfway through the very last chapter of the series, even though Maeda had confessed his love (several times in one day!) in an earlier chapter.
- The Corollary is painfully demonstrated in the Da Capo II anime - Koko confesses her feelings to Yoshiyuki at the end of the first episode. While he accepts and they go out for awhile, their relationship is rather strained, and eventually they break up at the end.
- This can be said for Love Hina with Keitaro and Naru.
- Subverted with Sakura's infamous fake love confession to Naruto in Chapter 469, which came after Hinata's sincere Anguished Declaration of Love in Chapter 437. Not only does Sakura's fake confession spectacularly fail to win, it explicitly loses—it is rejected outright, rightfully accused of not being emotionally honest because it was genuinely not an honest confession, and in retrospect, serves as the definitive Ship Sinking for NaruSaku.
- Inverted Trope with Sakura when she sincerely made her first love confession to Sasuke in a desperate attempt to prevent him from leaving the village. By the epilogue they are married and have a daughter, Sarada Uchiha.
- Ranma ½ is a classic example with Ranma and Akane.
- In the SHUFFLE! anime, it is played straight with Asa and Rin.
- Subverted and later Inverted in The World God Only Knows: While Ayumi was chronologically the last girl to openly confess to Keima in FLAG 187, she doesn't actually end up with him, thus subverting the trope; FLAG 267 (the penultimate chapter) then inverts this with Keima going for his second directly serious confession within the entire story: to Chihiro.