KAIS vs. MUYI (NAYICI) Mechanical Fidget Slider Engineering Guide:
POPO PEI/PEEK Liners, Lucky Candy Tuning Forks, Demoman & Kar98k Musketeer

How KAIS evolved from Cantonese auspicious magnetic sliders into zero-tuning POPO PEI/PEEK mechanical tracks and Lucky Candy tuning-fork liners, why MUYI officially rebranded to NAYICI, and why MOT Groove owners cross-shop the Kar98k-inspired Musketeer and grenade-profile Demoman compound sliders.

When collectors step up to high-performance mechanical sliders in our Fidget Slider Complete Guide, two studios define opposite ends of the engineering spectrum: KAIS and MUYI (now officially rebranded as NAYICI). KAIS is the undisputed master of internal liner acoustics and out-of-the-box slide refinement, whereas MUYI / NAYICI leads the industry in tactical firearm and ordnance-styled multi-mechanism compound fidgets.

This dossier brings together our founder’s first-hand workshop notes, internal liner material analysis, unedited acoustic bench videos, and strict teardown safety boundaries across 37 verified in-stock KAIS and MUYI / NAYICI listings.

KAIS first established its foothold in the precision EDC industry with magnetic sliders named after traditional Cantonese symbols of good fortune. Its breakout line, KAIS Lucky Candy, takes its name and wrapped-candy silhouette from the auspicious Lunar New Year candy gifted across Guangdong to wish friends good luck coming their way. KAIS followed that success with KAIS RUYI, named after the classic Chinese emblem of good wishes fulfilled.

As slider inner-liner engineering advanced across the industry, KAIS continuously upgraded both platforms rather than leaving them in the magnetic era:

1. From magnetic RUYI to mechanical RUYI RS and RUYI-S: KAIS adapted the ergonomic curved waist of the original RUYI into crisp multi-detent mechanical track sliders.

2. Acoustic tuning-fork inner liners on Lucky Candy: KAIS introduced specialized tuning-fork inner liners for the Lucky Candy line (Lucky Candy Crystallized Zirconium, Crystallized Titanium, and Mokuti), turning every slide into a bright, ringing metallic note.

In 2025, KAIS launched the KAIS POPO mechanical track slider. Originally unveiled as an exhibition early-release edition, its factory stock configuration stunned players on the show floor with its immediate smoothness and acoustic clarity, prompting KAIS to expand the platform into the full POPO and POPO RS family.

What makes POPO so good straight out of the box? Just as we noted in our EDC Fidget Materials Guide, more and more top studios now favor PEI (Ultem) and PEEK as internal slider liner materials because their low friction and crisp acoustic snap beat bare metal-on-metal contact. Newcomers can pick any slider in the KAIS POPO family and enjoy top-tier mechanical play immediately without ever opening the shell to tune springs or beads.

First, an essential entity note for collectors searching Google or AI shopping assistants: MUYI has officially rebranded its studio name to NAYICI. Whether a piece in our catalog carries the legacy MUYI stamp or the newer NAYICI stamp, it comes from the exact same tactical design studio.

Why do so many collectors who love MOT sliders (like the MOT Groove or Rhythm) end up cross-shopping MUYI / NAYICI? Because MOT sliders are pure single-mechanism track instruments, not compound multi-mechanism toys. Whenever a MOT player wants to branch out and experience a true compound fidget toy that packs multiple sliding, ratcheting, and bolt-cycling actions into one tactical chassis, they turn directly to MUYI / NAYICI.

Every flagship in the MUYI / NAYICI lineup channels tactical firearm and heavy ordnance mechanics:

The MUYI Musketeer (available in retail trims as well as 1-of-1 Damasteel and Zirconium vault pieces) has been one of the studio’s perennial bestsellers. Its multi-directional bolt travel takes direct inspiration from cycling the bolt of the iconic 98K (Kar98k) rifle in classic video games, delivering a deeply satisfying bolt-chambering rush on every stroke.

Shaped like a fragmentation hand grenade, the MUYI Demoman (plus Demoman Limited Edition and NAYICI Demoman Zirconium) aggregates multiple independent fidget mechanisms into one armored shell. Alongside the heavy-caliber Artillery, Bomber, and NAYICI Bone Breaker, it defines the tactical ordnance aesthetic.

If you landed on a sold-out pre-owned listing from Google Shopping, use these verified in-stock 1:1 tactile twins: for the sold-out KAIS POPO RS, step directly into the KAIS POPO Retail Series (198 in stock) or KAIS POPO PEI 1-of-1 Vault; for sold-out MUYI Bullet Nest Superconductor or Musketeer Mokume grails, inspect the Demoman Limited Edition, Musketeer Damasteel 1-of-1, or MUYI Artillery.

Before you put a screwdriver to a KAIS or MUYI / NAYICI slider, follow our workshop’s two golden rules:

1. Never blindly disassemble MUYI / NAYICI compound sliders (Musketeer, Demoman, Artillery): Because these are multi-mechanism compound fidgets packed with nested detents, bolt linkages, and micro-springs, unscrewing the shell without watching an official step-by-step teardown video first almost always results in launched springs or jammed tracks. Always contact TRB Creation support before opening any compound MUYI / NAYICI toy.

2. KAIS RUYI and Lucky Candy are safe for careful DIY spring and bead swaps: Their two-plate track geometry is straightforward, allowing you to open them over a parts tray to test different springs and detent balls. And if you pick the KAIS POPO, you never need to open it at all—its factory PEI and PEEK inner liner setup is already dialed in. See our Metal Fidget Toy Cleaning & Maintenance Guide for routine care.

Use our founder’s direct buyer matrix to pick the exact KAIS or MUYI / NAYICI model for your play style:

#1 KAIS Straight Call · In Stock KAIS POPO: PEI & PEEK Liner Mechanical Slider View listing #1 MUYI Grail Call · With Video MUYI (NAYICI) Demoman Grenade Compound Slider View listing Kar98k Bolt-Action Icon · In Stock MUYI (NAYICI) Musketeer Tactical Slider View listing Tuning-Fork Inner Liner · In Stock KAIS Lucky Candy: Auspicious Cantonese Series View listing Mechanical Track Evolution · In Stock KAIS RUYI RS Mechanical Track Slider View listing #1 MUYI Entry Call · In Stock MUYI (NAYICI) Eraser Compact Mechanical Slider View listing

Pair this KAIS vs. MUYI (NAYICI) comparison with our category pillar guides and studio engineering files:

Category Pillar Guides: Read our Fidget Slider Complete Guide: Magnetic vs. Mechanical Track, Fidget Spinner Complete Guide, EDC Fidget Materials & Finishes Guide, and How to Buy Certified Pre-Owned Metal Fidget Toys Safely.

Studio & Series Teardowns: Explore our ACEdc Complete Engineering Guide, JUZHEDC Complete Engineering Guide, MOT Rhythm & Groove Family Guide, DZ Top-B Series Guide, and LAUTIE Choc Engineering Guide. Browse live stock in All Fidget Sliders, Certified Pre-Owned Sliders, and All Pre-Owned EDC.

Choose KAIS POPO (or exotic Lucky Candy and RUYI RS editions) when you want silky PEI/PEEK inner liners and tuning-fork acoustics that play perfectly out of the box. Choose MUYI / NAYICI Eraser, the Kar98k-inspired Musketeer, or the grenade-profile Demoman when you want heavy tactical ordnance and multi-mechanism compound action.

Last updated: November 7, 2026. All inner-liner comparisons, brand lineage notes, and stock statuses are verified against live TRB Creation vault inventory at publication.