The Rapier is the second Sword blade and the fourth guaranteed blade available without drops (after Gastraph Bow and before Spear). It is the first of only three Starting Weapons that are capable of superior combinations with other swords; the other two being Broad Sword and Glaive (Scramasax also, but is extremely problematic). The rest of the Starting Weapons are usable only to devolve higher-Tier weapons. Even though it is the third blade of a weapon Design, it is included in the Starting Weapons mostly because it is found so early, but also because of its unusual Type, and the fact that it is able to make a Progression, a superior combination with the first Tier Sword. This irregular (non-consecutive, 1st and 3rd tier) recipe combines Spatha with Rapier to make a Short Sword. IRON Spathas will not be able to be combined with BRONZE Rapier into a HAGANE Short Sword until later when the more advanced Workshop is found, but they drop at the low rate of 8/255 from enemies in the Wine Cellar, Catacombs and Sanctum. One Zombie Fighter that appears in Smokebarrel Stair in the Wine Cellar after Ashley visits Room of Cheap Red Wine drops a Bronze Spatha at 16/255. Another appears on a Zombie Fighter in Room of Rotten Grapes much later, after Ashley kills the Lich in Undercity East. The combination between Rapier, a third Tier Sword, and Spatha, a first Tier, is an irregular one, with Spatha taking the place of Scimitar, the second Tier. This makes Spatha a Volunteer of the Usurper type. Firangi cannot be made from Short Sword, and Firangi does not drop until Underdark Fishmarket in Undercity West.
Rapier is acquired in the Room of Cheap Red Wine in the Wine Cellar; unlike most of the Starting Weapons, that come from chests, it is instead a 100% drop. It drops at a 255/255 rate (always) from Ashley's first encounter with the Undead, both victims and tools of the Death Magic of Lea Monde known by Ivalice's people, somewhat erroneously, as the Dark.
Rapier is the only Pierce Type Sword. This may well be to stand in for Daggers until the game is in a late enough stage that the SILVER Scramasax coolness factor of "Soul Kiss" does not overwhelm it. No sense in giving everything away at once. Rapier can be put to good use straight away; Bat, Silver Wolf and Hellhound enemies are all weaker to Pierce than the other Types of damage. If following the other Three Weapons strategy, this would make Rapier designated a Beast / Dragon weapon. This is ideal, as Dragons are almost uniformly weakest to Pierce. However, it would also mean that the Rapier or its descendants would one day have to merge with the Dagger or Polearm Design line, to keep Pierce Type damage.
The Grip the Rapier comes with should be replaced with the zero-gem Swept Hilt found on the later "Shandy Gaff" Broad Sword, and other Hilts that are high in Pierce, balanced with considerations of Gems. Class, Affinity and Type are all divided by four hundred and then multiplied by total Strength to determine Damage. For example, Swept Hilt has zero Blunt, six Edged, and two Piercing, for up to 1.5% times total Strength, compared with 3.75% for Minor Elemental gems such as Sylphid Topaz, and the same for Minor Nemesis gems such as Iocus.
A second, IRON Rapier is a 100% drop from Sarjik, one of the Crimson Blades accompanying Duane at Tircolas Flow in Town Center West. Nearby, in Town Center West, is the Magic Hammer workshop, where the Iron Rapier can be combined with the BRONZE one to make a HAGANE one. Material, though, should be of secondary consideration next to Class and Affinity bonuses. There are only two other Rapier drops in the whole game: in The Rene Coastroad and Sewer of Ravenous Rats
It is not possible to integrate the Starting Weapons other than the SILVER Scramasax "Soul Kiss" Dagger into any combinations with Damascus until the New Game Plus, when the Godhands workshop is accessed.
With so few weapons to choose from at the start of the game, it is likely that this blade will acquire a great deal of Class bonuses, so it is worthwhile searching for a good combine target. Progression in the Sword Design line with Rapier and Short Sword is highly recommended.
Although the Rapier can be improved very early, the second improvement does not come until much later. This is one of very few and weak reasons for making a Mismatch to change this Sword into another Design. If this course, which is not recommended, be taken, and since Polearms are somewhat rare, perhaps a combination of a Sabre Mace Heavy Mace with Rapier to get a Glaive. A low-Tier result. Heavy Maces are common and have very few tiers.