Obtain nothing. That is our current system. Does that mean we deserve something for achievements? Not necessarily, but it would be an incentive to do them. As seen above there could be more achievements to improve upon the idea of obtaining higher ranked equipment rather than several low tier weapons. To analyze the original post:

The sword accessory we already have is fine. What they could do instead is give us a Prismatic design one for a sword related achievement described below.

A bandolier of boolits has already been suggested though I assume the reason it has been ignored thus far is because of the model motion issue; does it become directly attached to the armor and match its movement or is it somewhat static? Again, see below for "new" achievements.

We already have enough of those costumes. Twenty-four since I last counted. See below for the same reasons as above.

I have to admit, this one fits well to its achievement; not anyone can accumulate that many minerals. It literally comes down to grinding out all those floors for a long time, though being in parties contributes significantly. Either a badge with the mineral symbol or the pack would befit this experience.

Sure. Not much I can comment on here because the achievement proves general competence enough to deserve something but not enough to have something spectacularly amazing which makes your eyeballs go back in your head and tell your brain in person what it just saw.

Alright, for the three weapon achievements we have an obvious issue: all they require is having a certain amount of weapons. Not certain weapon types, a certain amount. The following rewards are obviously untradable to prevent accessory farming and what not. "What do you propose, nose?" Stay on your toes, bros, while I lay a hose. That was horrible.

For swords we already have a short sword accessory. In fact we have two; parrying and side. The former is often used for surprise attacks at close range when the opponent does not expect the Spanish Inquisition and the latter used in case the sword that was in your hand is rendered useless. The latter is going to be what we base this accessory on. We are all familiar with the variety in swords, more specifically the major lines: Calibur, Brandish, Flourish, Troika, Sealed, Cutter, and maybe Snarble Barb. Snarble and Flourish lines are very similar but not necessarily the same so they may as well be included for going from 2* to 5*. For this achievement the user must obtain at least one 5* variant of each of the previously stated weapon lines to obtain a gilded side blade. This means they can have either Leviathan or Vanquisher, any of the 5* Brandish lines, any of the 5* Flourishes, either of the 5* Troikas, either of the 5* Sealed lines, either of the 5* Cutter lines, and Barbarous Thorn Blade because it is forever alone in its alchemy line. If Winmillion were buffed we could include it but have the achievement demands its 4* variant unless they create a 5* for it. That means seven 5* swords if Winmillion is excluded to the corner of shame.

Boolit. I love typing, saying, and reading that word. I say it at my desk and people give me weird expressions. Then I take the revolver in the drawer out and shoot them in the head. I was kidding, stop calling the cops. Not that they would be able to do anything. Honk honk. What was next, the gun one? Same idea as the sword one, but with one stipulation: you only need one of the several Alchemer lines. For the boolit/bullet belt accessory achievement you need the following: one 5* Autogun (Blitz, Plague, Volcanic Pepperbox), one 5* Alchemer (Magma, Storm, Hail, Nova, Umbra), one 5* Magnus (Callahan, Iron Slug), Valiance, one 5* Antigua (Peacemaker, Sentenza), one 5* Pulsar (Polaris, Supernova), and one 5* Catalyzer (Biohazard, Neutralizer). It could be two 5* Alchemers since they have more variety but we already have seven 5* guns to obtain here.

The bomb one is going to drop the metaphorical and literal bomb on do-want. For the accessory itself we already have the Blast bandolier, but what do the versatile bombers get? The same thing. No. Enough of this tyranny. Enough of these snakes on this plane. The bandolier itself would have the 2* Spine Cone, a 2* Vaporizer (most likely Static or Freezing, the more commonly used ones), and a 3* Graviton. For the achievement itself you need the following: at least two 5* Blast lines (Nitronome, Irontech, Big Angry), Barrage, at least two 5* Vaporizer lines (Agni, Shivermist, Voltaic, Venom, Stagger), one of the 5* suction lines (Graviton, Electron), and one of the shard lines at 4* (Radiant, Ionized). This also adds up to seven weapons to obtain.

I still remember the whip and miniboss threads from Verodius. I have them in my index of stuff and have included the current thread. I can never forget what is recorded where I do not delete. I can also never forget the Alamo.