diff --git a/apps/readest-app/src/__tests__/document/paginator-vertical-rl.browser.test.ts b/apps/readest-app/src/__tests__/document/paginator-vertical-rl.browser.test.ts
new file mode 100644
index 00000000..2f09b085
--- /dev/null
+++ b/apps/readest-app/src/__tests__/document/paginator-vertical-rl.browser.test.ts
@@ -0,0 +1,282 @@
+import { describe, it, expect, beforeAll, afterEach } from 'vitest';
+import { DocumentLoader } from '@/libs/document';
+import type { BookDoc } from '@/libs/document';
+import type { Renderer } from '@/types/view';
+
+// Regression tests for readest#624: books with writing-mode: vertical-rl
+// (Japanese/Chinese vertical text) must turn pages horizontally like printed
+// vertical books. CSS fragmentation stacks vertical-rl pages top-to-bottom, so
+// the scroll axis stays vertical internally, but the page-turn INPUTS are
+// horizontal (swipe right = next for vertical-rl) and turns swap instantly
+// instead of sliding along the vertical scroll axis.
+
+const VERTICAL_EPUB_URL = new URL('../fixtures/data/sample-vertical-rl.epub', import.meta.url).href;
+const HORIZONTAL_EPUB_URL = new URL('../fixtures/data/sample-alice.epub', import.meta.url).href;
+
+// The paginator's swipe entry point isn't part of the app-facing Renderer type.
+type SwipePaginator = Renderer & {
+  snap: (vx: number, vy: number, dx: number, dy: number, dt: number) => void;
+};
+
+let verticalBook: BookDoc;
+let horizontalBook: BookDoc;
+let getDirection: (doc: Document) => { vertical: boolean; rtl: boolean };
+
+const loadEPUB = async (url: string, name: string) => {
+  const resp = await fetch(url);
+  const buffer = await resp.arrayBuffer();
+  const file = new File([buffer], name, { type: 'application/epub+zip' });
+  const loader = new DocumentLoader(file);
+  const { book } = await loader.open();
+  return book;
+};
+
+const waitForStabilized = (el: HTMLElement, timeout = 10000) =>
+  new Promise<void>((resolve, reject) => {
+    const timer = setTimeout(() => reject(new Error('stabilized timeout')), timeout);
+    el.addEventListener(
+      'stabilized',
+      () => {
+        clearTimeout(timer);
+        resolve();
+      },
+      { once: true },
+    );
+  });
+
+const wait = (ms: number) => new Promise((r) => setTimeout(r, ms));
+
+/** Poll until the paginator lands on the expected page or timeout. */
+const waitForPage = async (el: Renderer, page: number, timeout = 3000) => {
+  const start = Date.now();
+  while (Date.now() - start < timeout) {
+    if (el.page === page) return;
+    await wait(50);
+  }
+};
+
+describe('Vertical-rl pagination (browser)', () => {
+  let paginator: SwipePaginator;
+
+  beforeAll(async () => {
+    verticalBook = await loadEPUB(VERTICAL_EPUB_URL, 'sample-vertical-rl.epub');
+    horizontalBook = await loadEPUB(HORIZONTAL_EPUB_URL, 'sample-alice.epub');
+    ({ getDirection } = (await import('foliate-js/paginator.js')) as unknown as {
+      getDirection: (doc: Document) => { vertical: boolean; rtl: boolean };
+    });
+  }, 30000);
+
+  const createPaginator = () => {
+    const el = document.createElement('foliate-paginator') as SwipePaginator;
+    Object.assign(el.style, {
+      width: '800px',
+      height: '600px',
+      position: 'absolute',
+      left: '0',
+      top: '0',
+    });
+    document.body.appendChild(el);
+    return el;
+  };
+
+  const setup = async (book: BookDoc, index = 0) => {
+    paginator = createPaginator();
+    paginator.open(book);
+    const stabilized = waitForStabilized(paginator);
+    await paginator.goTo({ index });
+    await stabilized;
+  };
+
+  afterEach(async () => {
+    if (paginator) {
+      await new Promise((r) => requestAnimationFrame(() => requestAnimationFrame(r)));
+      try {
+        paginator.destroy();
+      } catch {
+        /* iframe body may already be torn down */
+      }
+      paginator.remove();
+    }
+  });
+
+  it('marks vertical-rl documents as rtl in getDirection', async () => {
+    await setup(verticalBook);
+    const contents = paginator.getContents();
+    const doc = contents[0]!.doc;
+    expect(getDirection(doc)).toEqual({ vertical: true, rtl: true });
+  });
+
+  const makeTouch = (x: number, y: number) =>
+    new Touch({ identifier: 1, target: paginator, screenX: x, screenY: y, clientX: x, clientY: y });
+
+  const fireTouch = (type: string, x: number, y: number) =>
+    paginator.dispatchEvent(
+      new TouchEvent(type, {
+        bubbles: true,
+        cancelable: true,
+        touches: type === 'touchend' ? [] : [makeTouch(x, y)],
+        changedTouches: [makeTouch(x, y)],
+      }),
+    );
+
+  const viewTransform = () => {
+    const container = paginator.shadowRoot!.getElementById('container')!;
+    const child = container.children[0] as HTMLElement | undefined;
+    const transform = child && getComputedStyle(child).transform;
+    return transform && transform !== 'none' ? new DOMMatrix(transform) : null;
+  };
+
+  it('tracks the finger horizontally during a drag', async () => {
+    await setup(verticalBook);
+    paginator.setAttribute('animated', '');
+    const page = paginator.page;
+
+    let x = 700;
+    fireTouch('touchstart', x, 400);
+    for (let i = 0; i < 5; i++) {
+      x += 30;
+      fireTouch('touchmove', x, 400);
+      await wait(16);
+    }
+    // Mid-drag the page follows the finger to the right, horizontally only.
+    const midDrag = viewTransform();
+    expect(midDrag).not.toBeNull();
+    expect(midDrag!.m41).toBeGreaterThan(0);
+    expect(midDrag!.m42).toBe(0);
+
+    fireTouch('touchend', x, 400);
+    await waitForPage(paginator, page + 1);
+    expect(paginator.page).toBe(page + 1);
+  });
+
+  it('reverts an aborted drag without turning the page', async () => {
+    await setup(verticalBook);
+    paginator.setAttribute('animated', '');
+    const page = paginator.page;
+
+    let x = 700;
+    fireTouch('touchstart', x, 400);
+    for (let i = 0; i < 5; i++) {
+      x += 30;
+      fireTouch('touchmove', x, 400);
+      await wait(16);
+    }
+    expect(viewTransform()?.m41 ?? 0).toBeGreaterThan(0);
+    // Finger mostly returns, rests, then lifts: the drag is below the commit
+    // threshold and there is no flick, so the page must not turn.
+    for (let i = 0; i < 4; i++) {
+      x -= 30;
+      fireTouch('touchmove', x, 400);
+      await wait(16);
+    }
+    await wait(150);
+    fireTouch('touchend', x, 400);
+    await wait(400);
+    expect(paginator.page).toBe(page);
+    expect(viewTransform()?.m41 ?? 0).toBe(0);
+  });
+
+  /**
+   * Sample the mid-flight view transforms of a page turn, tagging each sample
+   * with the scroll offset it was taken at. The two-phase slide jumps the
+   * scroll at its midpoint, so samples at the starting offset belong to the
+   * exit phase and samples at any other offset to the enter phase.
+   */
+  const sampleTurn = async (startPos: number, timeout = 700) => {
+    const container = paginator.shadowRoot!.getElementById('container')!;
+    const exit: DOMMatrix[] = [];
+    const enter: DOMMatrix[] = [];
+    const t0 = performance.now();
+    while (performance.now() - t0 < timeout) {
+      const child = container.children[0] as HTMLElement | undefined;
+      const transform = child && getComputedStyle(child).transform;
+      if (transform && transform !== 'none') {
+        const m = new DOMMatrix(transform);
+        if (m.m41 !== 0 || m.m42 !== 0) {
+          (paginator.containerPosition === startPos ? exit : enter).push(m);
+        }
+      }
+      await new Promise((r) => requestAnimationFrame(r));
+    }
+    return { exit, enter };
+  };
+
+  it('slides pages horizontally (not along the scroll axis) when animated', async () => {
+    await setup(verticalBook);
+    paginator.setAttribute('animated', '');
+    const size = paginator.size;
+    const before = paginator.containerPosition;
+
+    const turn = paginator.next();
+    const forward = await sampleTurn(before);
+    // Forward in vertical-rl reads right-to-left: the outgoing page exits to
+    // the right and the incoming page enters from the left, horizontal only.
+    const forwardSamples = [...forward.exit, ...forward.enter];
+    expect(forwardSamples.length).toBeGreaterThan(0);
+    expect(forwardSamples.every((m) => m.m42 === 0)).toBe(true);
+    expect(forward.exit.every((m) => m.m41 > 0)).toBe(true);
+    expect(forward.enter.every((m) => m.m41 < 0)).toBe(true);
+    await turn;
+    expect(paginator.containerPosition).toBe(before + size);
+
+    const back = paginator.prev();
+    const backward = await sampleTurn(before + size);
+    const backwardSamples = [...backward.exit, ...backward.enter];
+    expect(backwardSamples.length).toBeGreaterThan(0);
+    expect(backwardSamples.every((m) => m.m42 === 0)).toBe(true);
+    expect(backward.exit.every((m) => m.m41 < 0)).toBe(true);
+    expect(backward.enter.every((m) => m.m41 > 0)).toBe(true);
+    await back;
+    expect(paginator.containerPosition).toBe(before);
+  });
+
+  it('swaps pages instantly when animation is disabled', async () => {
+    await setup(verticalBook);
+    const size = paginator.size;
+    const before = paginator.containerPosition;
+    await paginator.next();
+    expect(paginator.containerPosition).toBe(before + size);
+  });
+
+  it('turns to the next page on a rightward swipe (vertical-rl reads right-to-left)', async () => {
+    await setup(verticalBook);
+    const page = paginator.page;
+    // Finger moves right: vx/dx negative in the paginator's swipe deltas.
+    paginator.snap(-1.2, 0, -150, 0, 120);
+    await waitForPage(paginator, page + 1);
+    expect(paginator.page).toBe(page + 1);
+  });
+
+  it('turns back on a leftward swipe in vertical-rl', async () => {
+    await setup(verticalBook);
+    const page = paginator.page;
+    paginator.snap(-1.2, 0, -150, 0, 120);
+    await waitForPage(paginator, page + 1);
+    expect(paginator.page).toBe(page + 1);
+
+    // Finger moves left: vx/dx positive.
+    paginator.snap(1.2, 0, 150, 0, 120);
+    await waitForPage(paginator, page);
+    expect(paginator.page).toBe(page);
+  });
+
+  it('still pages forward on the legacy upward swipe for vertical books', async () => {
+    await setup(verticalBook);
+    const page = paginator.page;
+    // Finger moves up: vy/dy positive.
+    paginator.snap(0, 1.2, 0, 150, 120);
+    await waitForPage(paginator, page + 1);
+    expect(paginator.page).toBe(page + 1);
+  });
+
+  it('keeps leftward-swipe-to-advance for horizontal ltr books', async () => {
+    // Index 3 is the first chapter (multi-page); earlier spine items are
+    // single-page cover/title sections a swipe would step across.
+    await setup(horizontalBook, 3);
+    const page = paginator.page;
+    // Finger moves left: vx/dx positive → next page in ltr.
+    paginator.snap(1.2, 0, 150, 0, 120);
+    await waitForPage(paginator, page + 1);
+    expect(paginator.page).toBe(page + 1);
+  });
+});
diff --git a/apps/readest-app/src/__tests__/fixtures/data/sample-vertical-rl.epub b/apps/readest-app/src/__tests__/fixtures/data/sample-vertical-rl.epub
new file mode 100644
index 00000000..1b416883
Binary files /dev/null and b/apps/readest-app/src/__tests__/fixtures/data/sample-vertical-rl.epub differ
diff --git a/packages/foliate-js b/packages/foliate-js
index 0f857071..cecaef95 160000
--- a/packages/foliate-js
+++ b/packages/foliate-js
@@ -1 +1 @@
-Subproject commit 0f85707129f61f42ee7a9313b7bd58a2afd0432d
+Subproject commit cecaef95be787cfb135b3d9a68325d62676c8f58