[Empirical Study] How Much Did the "Favorite Face Top 9 (Suki-Gao Best 9)" Web App Boost Idol Follower Growth? A Statistical Analysis of 2,637 Idols

1. What Is the Viral "Female Idol Favorite Face Top 9 (Suki-Gao Best 9)" Phenomenon?

From late September through October 2026, a free browser-based diagnostic and collage tool called "Suki-Gao Shindan / Suki-Gao 9-Sen Maker (Favorite Face Top 9 / Best 9)" ignited an explosive viral wave across Japanese idol fandoms on X (formerly Twitter) and Instagram.

Setting aside vocal ability, variety skills, group fame, and even one's usual oshi (favorite member) allegiances, the tool asks users to intuitively tap or choose idols whose facial features and visual styling they purely prefer. In seconds, it generates a clean 3×3 grid image (Top 9 or Top 5) ready for social sharing.

Shared tens of thousands of times under hashtags like #女ドル好き顔9選 (#FemaleIdolFavoriteFaceTop9) and #国内女性アイドル好き顔TOP9, the tool does more than reveal a fan's subconscious visual type (e.g., puppy-eyed, cat-eyed, classic dark-haired, or cool beauty). Crucially, it functions as a massive "visual-first cross-fandom discovery engine"—where fans who normally only follow Sakamichi or =LOVE stumble upon members of KAWAII LAB. or underground live idol groups on the selection screen and fall in love at first sight.

To answer the core empirical question—"Since the Favorite Face Best 9 app was released, by what percentage (%) did idols' follower growth accelerate compared to normal, and is there a statistically significant difference between registered and unregistered members?"—the IdolSpike Analytics Editorial Team conducted a full-scale statistical investigation across 2,637 active domestic female idols tracked daily in the IdolSpike database.

---

2. [Overall Verification] By What Percentage (%) Did Follower Growth Accelerate Immediately, 1 Week, and 18 Days After Release?

First, we examined the 203 female idols with tracked individual X accounts (222 across total SNS) who were included in the initial release cohort of the female idol maker (launched September 28, 2026, with the cross-group edition scaling on October 1 across 7 categories: Sakamichi, 48G, Hello! Project, KAWAII LAB., IkonoiJoy, LIVE PLANET, and FreeK). We compared their "Pre-Release 7-Day Baseline (Sept 21–28)" against post-release windows (Immediate 3 Days, 1 Week After, Week 2, and Full 18-Day Cumulative).

Key Finding: Follower Growth Accelerated by "+62.7% to +95.6%" After 1 Week, and "+107.0% to +157.4% (Over 2x)" Across 18 Days!

The empirical trajectory reveals a three-stage viral cascade:

1. Immediate 3 Days (Sept 28–Oct 1): This served as the "seeding phase" where early adopters generated and posted their 3×3 grids. While overall average daily speed remained near baseline (+0.0414%/day), within the domestic major idol category, registered members already outperformed unregistered peers by +41.5% (p < 0.0001) during these first 72 hours.

2. 1 Week After Release (Sept 28–Oct 5): Once thousands of 3×3 grids flooded X timelines, followers began asking, "Who is the girl in the middle row?" and searching for her account. Weekly growth jumped from +0.292% to +0.475%—meaning idols grew +62.7% faster than usual in percentage terms (+82.2% more new followers per week in headcount: 327.9 vs. 179.9, and +95.6% faster when averaging each member's individual acceleration ratio).

3. Week 2 (Oct 5–12) & Full 18 Days (Sept 28–Oct 16): Fueled by the site's aggregated "Everyone's Favorite Face Ranking" and analytical columns, Week 2 growth surged to +0.680% (+133.1% above baseline / 2.33x). Across the entire 18-day post-release window, daily follower velocity averaged +0.0862%/day—a +107.0% increase (2.07x) over normal, with individual member acceleration averaging +157.4% (2.57x).

---

3. [Statistical Significance] Registered Members vs. Unregistered Members (Welch's t-Test)

Could this surge simply reflect a broader October tailwind across the entire idol industry? To test this hypothesis rigorously, we compared members registered in the Favorite Face Top 9 app against unregistered members over the exact same dates and performed Welch's two-sample t-tests.

An important methodological note: among the ~2,000 unregistered idols in IdolSpike, the vast majority are smaller indie/live idols with only a few thousand followers (where gaining 20 followers yields a high percentage), whereas registered members include many major idols with 50,000 to 500,000+ followers. To eliminate this denominator-size confounding (Simpson's paradox), we conducted (1) a direct comparison within the Domestic Major Idol category and (2) follower-bracket matched comparisons.

① Domestic Major Idols: Registered (n=93) vs. Unregistered (n=179)

Within the domestic major category, the divergence between registered and unregistered members is statistically indisputable: t = +6.68 (p < 0.0001) in the first 3 days, t = +5.10 (p < 0.0001) at 1 week, and t = +4.02 (p < 0.0001) over 18 days. Prior to launch, registered major members grew 1.22x faster than unregistered peers; after launch, that lead expanded to 1.62x in Week 1 and 1.76x in Week 2, with registered members gaining 5.09x more followers (+2,167.4 vs. +426.2) over 18 days.

② Follower-Bracket Matched Comparison: Registered vs. Unregistered (18 Days Post-Release)

Comparing members within identical X follower brackets across both major and live idol scenes confirms the effect holds regardless of account size:

The strongest statistical separation (t = +2.81, p < 0.01) occurs in the 50,000–150,000 follower bracket (Mid-Major / Breakout Tier), where registered idols accelerated by +208.3% (3.08x) over their pre-release baseline and achieved 1.86x the growth rate of unregistered peers (+1.607% vs. +0.864%). This proves that while household-name stars benefited strongly, the biggest beneficiaries of visual discovery were rising mid-tier idols whose faces captivated users outside their existing fanbase.

---

4. Genre-by-Genre Breakdown: Every Initial Genre Accelerated by "+29% to +228%"!

Comparing the 7 initial genres launched on September 28 against the HEROINES roster (which was added later on October 13) provides a textbook natural experiment:

Every single one of the 7 initial genres saw their daily follower growth pace accelerate significantly after launch (1.29x to 3.28x normal speed). Meanwhile, HEROINES (iLiFE!, TENRIN, MEGAFON, etc.) continued to grow steadily in total followers (+0.402% in 1 week and +0.948% over 18 days; e.g., Aisu +1,830 followers, Riri Kokohana +1,346 followers), but because the collective was not included in the September 28 launch and was only added on October 13 following fan requests, it did not experience the 2x–3x acceleration spike during the Sept 28–Oct 12 window—confirming as a natural control group that inclusion in the initial September 28 launch was the decisive catalyst behind the early October growth multiplier.

---

5. [Member-by-Member Comparison] 3-Day, 7-Day, and 18-Day Follower Trajectories Across 28 Featured Idols

How did individual idols who topped the "Favorite Face Top 9" rankings perform after the app's release? Below is the complete empirical breakdown across 28 representative idols from IdolSpike's daily logs:

---

6. Three Structural Mechanisms Behind the "Favorite Face Best 9" Follower Surge

Why did a fan-made visual quiz generate such a dramatic, statistically significant surge in follower growth (2x to 10x+ above normal pace)? Three structural mechanisms explain the phenomenon:

① The Cross-Genre Hub Effect Exemplified by Maika Sasaki, Iori Noguchi, and Kotomi Tachibana

In the all-genre female idol maker, the top three most-selected faces were Maika Sasaki (=LOVE, 33.4% pick rate), Iori Noguchi (=LOVE, 25.1%), and Kotomi Tachibana (CANDY TUNE, 16.4%).

Kotomi Tachibana (CANDY TUNE) illustrates the cross-pollination effect most vividly: her weekly X gain jumped from +168 (+0.23%) pre-release to +411 (+0.55%, +144% faster) one week after launch, and +1,423 (+1.92%, +229% faster / 3.29x) over 18 days. Fans who opened the all-genre quiz intending to pick Sakamichi or =LOVE members were repeatedly exposed to Tachibana's visual portrait in diagnostic rounds and shared 3×3 grids, converting into brand-new followers across agency lines.

② Explosive Synergy Between TikTok Audio Virality and Face-to-Name Matching (CUTIE STREET)

Members of CUTIE STREET—including Ayano Masuda (#1 in KAWAII LAB., 57.0% pick rate), Emiru Kawamoto (#3, 51.6%), Aika Sano (#4), and Haruka Sakuraba (highest #1-rank rate at 20.0%)—saw their growth rates skyrocket from ~+0.20%/week pre-release to +1.34%–+1.41% (+428% to +712% faster) after 1 week, and +5.90%–+5.97% (+5,800 to +11,500 new followers; 8.6x to 13.8x faster than baseline) over 18 days. For casual listeners who already knew their viral TikTok tracks, the 9-grid tool served as the decisive bridge that matched each member's face with her name and personal X handle.

③ Underdog Discovery for Live Idols (VVSiS, Pretty Chuu, Nekopura pixx.)

For underground and live idols who rarely appear on national television, being displayed side-by-side with Nogizaka46 and =LOVE in a purely visual tournament leveled the playing field. Ayasa Natsuhane (VVSiS, #1 in LIVE PLANET) accelerated by +894% (9.94x normal pace, +1,537 followers), Woyuta Yuno (VVSiS, #2) by +725% (8.25x), Momo Mochizuki (Pretty Chuu, #3) by +96% (1.96x), and Mii Masuda (Nekopura pixx., #2 in FreeK) by +166% (2.66x).

---

7. Conclusion: Visual UGC Tools Are the New Social Recommendation Engine

Summarizing IdolSpike's empirical study of 2,637 domestic female idols:

1. How Much Faster Did Idols Grow?:

Idols registered in the initial launch of "Favorite Face Top 9" (n=203) grew +62.7% faster than usual (+82.2% in follower headcount; +95.6% in mean individual acceleration) in Week 1, +133.1% faster (2.33x) in Week 2, and +107.0% faster per day (2.07x; +157.4% mean individual acceleration) across the full 18-day post-release window.

2. Statistically Significant Advantage Over Unregistered Idols:

Within the domestic major category, registered members outperformed unregistered peers by 1.42x in 3 days (t=6.68, p<0.0001), 1.62x in 1 week (t=5.10, p<0.0001), and 1.72x in rate / 5.09x in headcount over 18 days (t=4.02, p<0.0001). In the 50k–150k follower bracket, registered idols achieved 1.86x the growth rate of unregistered peers (t=2.81, p<0.01).

3. Both "Broad Consensus Visuals" and "High #1-Ratio Icons" Drive Conversion:

Whether through universal visual appeal (Maika Sasaki, Ayano Masuda) or intense #1-pick devotion (Iori Noguchi, Haruka Sakuraba, Ruka Nakagawa), fan-curated 3×3 visual grids have emerged in 2026 as one of the most powerful organic discovery funnels in the Japanese idol ecosystem.