Every chapter has a title (helper,castaways...) and a number signifying how far we are in that title, Fin means it's the final time we see the "helper" title, these titles are not consecutive so chapter 16 is castaways 13(not Fin) but chapter 17 is target 1, then we continue the castaway title in chapter 135(castaway 14), see end of chapter 128 for the other titles