diff --git a/.zed/tasks.json b/.zed/tasks.json
index 4868825..34420e6 100644
--- a/.zed/tasks.json
+++ b/.zed/tasks.json
@@ -1,9 +1,10 @@
-// Static tasks configuration.
-//
-// Example:
 [
   {
     "label": "Test",
     "command": "deno test"
+  },
+  {
+    "label": "Test - Watch",
+    "command": "deno test --watch"
   }
 ]
diff --git a/deno.json b/deno.json
index 9bd54fd..ffdf2b3 100644
--- a/deno.json
+++ b/deno.json
@@ -1,8 +1,9 @@
 {
   "name": "@textplace/core",
-  "version": "0.2.0",
+  "version": "0.4.1",
   "exports": "./mod.ts",
   "imports": {
-    "@deno/dnt": "jsr:@deno/dnt@^0.41.3"
+    "@deno/dnt": "jsr:@deno/dnt@^0.41.3",
+    "@std/cli": "jsr:@std/cli@^1.0.11"
   }
 }
diff --git a/deno.lock b/deno.lock
index 491b9f0..afae4c4 100644
--- a/deno.lock
+++ b/deno.lock
@@ -7,6 +7,7 @@
     "jsr:@std/assert@0.223": "0.223.0",
     "jsr:@std/assert@0.226": "0.226.0",
     "jsr:@std/bytes@0.223": "0.223.0",
+    "jsr:@std/cli@^1.0.11": "1.0.11",
     "jsr:@std/fmt@0.223": "0.223.0",
     "jsr:@std/fmt@1": "1.0.3",
     "jsr:@std/fs@0.223": "0.223.0",
@@ -54,6 +55,9 @@
     "@std/bytes@0.223.0": {
       "integrity": "84b75052cd8680942c397c2631318772b295019098f40aac5c36cead4cba51a8"
     },
+    "@std/cli@1.0.11": {
+      "integrity": "ec219619fdcd31bcf0d8e53bee1e2706ec9a02f70255365a094f69755dadd340"
+    },
     "@std/fmt@0.223.0": {
       "integrity": "6deb37794127dfc7d7bded2586b9fc6f5d50e62a8134846608baf71ffc1a5208"
     },
@@ -151,7 +155,8 @@
   },
   "workspace": {
     "dependencies": [
-      "jsr:@deno/dnt@~0.41.3"
+      "jsr:@deno/dnt@~0.41.3",
+      "jsr:@std/cli@^1.0.11"
     ]
   }
 }
diff --git a/logic/board.ts b/logic/board.ts
index eeb8765..0436cdc 100644
--- a/logic/board.ts
+++ b/logic/board.ts
@@ -9,15 +9,7 @@ import { applyChange, createSection } from "./section.ts";
 import type { BoardChange } from "../types/change.ts";
 
 export function createBoard(config: BoardConfig): BoardData {
-  const sections: SectionData[][] = Array(config.ySections)
-    .fill(0)
-    .map((_, sy) =>
-      Array(config.xSections)
-        .fill(0)
-        .map((_, sx) => createSection({ sx, sy }, config))
-    );
-
-  return { config, sections };
+  return { config, sections: [] };
 }
 
 export function locateSection(
@@ -30,9 +22,38 @@ export function locateSection(
   };
 }
 
+/**
+ * Get a section from board.
+ *
+ * If the section does not exist yet, it will be created and (optionally) added to `board`.
+ */
+export function getSectionOnBoard(
+  { sx, sy }: SectionPosition,
+  board: BoardData,
+  options: {
+    /**
+     * Whether the section data is only used for reading.
+     *
+     * If `true`, this function will return an empty section configured with default values, but will not add it to the board data to save storage.
+     */
+    readOnly: boolean;
+  } = { readOnly: false },
+): SectionData {
+  let section: SectionData;
+  if (!board.sections[sy] && !options.readOnly) board.sections[sy] = [];
+
+  if (!board.sections[sy]?.[sx]) {
+    section = createSection({ sx, sy }, board.config);
+    if (!options.readOnly) board.sections[sy][sx] = section;
+  } else {
+    section = board.sections[sy][sx];
+  }
+  return section;
+}
+
 export function applyChangeOnBoard(change: BoardChange, board: BoardData) {
-  const { sx, sy } = locateSection(change, board.config);
-  const section = board.sections[sy][sx];
+  const sPos = locateSection(change, board.config);
+  const section = getSectionOnBoard(sPos, board);
   applyChange(change, section);
 }
 
@@ -59,8 +80,8 @@ export function renderFullBoard(data: BoardData): FullBoard {
         continue;
       }
 
-      const { sx, sy } = locateSection({ x, y }, data.config);
-      const section = data.sections[sy][sx];
+      const sPos = locateSection({ x, y }, data.config);
+      const section = getSectionOnBoard(sPos, data, { readOnly: true });
       const xInSection = x % data.config.sectionWidth;
       const yInSection = y % data.config.sectionHeight;
 
@@ -85,9 +106,9 @@ export function renderFullBoard(data: BoardData): FullBoard {
   return {
     w: lineLength,
     h: totalLineCount,
-    ch: ([] as string[]).concat(...chLines).flat(),
-    color: ([] as string[]).concat(...colorLines).flat(),
-    bg_color: ([] as string[]).concat(...bgColorLines).flat(),
-    width: ([] as number[]).concat(...widthLines).flat(),
+    ch: chLines.flat(),
+    color: colorLines.flat(),
+    bg_color: bgColorLines.flat(),
+    width: widthLines.flat(),
   };
 }
diff --git a/logic/character.ts b/logic/character.ts
index d1b9f69..2d58dac 100644
--- a/logic/character.ts
+++ b/logic/character.ts
@@ -1,7 +1,6 @@
+import { unicodeWidth } from "@std/cli/unicode-width";
+
 const segmenter = new Intl.Segmenter("en", { granularity: "grapheme" });
-const cjkRegex =
-  /[\p{Unified_Ideograph}\u30A0-\u30FF\u3040-\u309F\u31F0-\u31FF]/u;
-const printableASCIIRegex = /^[\x20-\x7E]$/;
 
 export function getCharacterWidth(ch: string): number {
   const segments = [...segmenter.segment(ch)];
@@ -11,11 +10,6 @@ export function getCharacterWidth(ch: string): number {
     );
   }
 
-  const matchesASCII = ch.match(printableASCIIRegex);
-  const matchesCJK = ch.match(cjkRegex);
-
-  if (!matchesASCII && !matchesCJK) throw new Error(`Invalid character: ${ch}`);
-
-  // TODO: Support Emojis.
-  return matchesCJK ? 2 : 1;
+  // TODO: Properly fix this.
+  return Math.min(unicodeWidth(ch), 2);
 }
diff --git a/logic/section.ts b/logic/section.ts
index d935dc3..c3f976c 100644
--- a/logic/section.ts
+++ b/logic/section.ts
@@ -16,17 +16,17 @@ export function createSection(
   const offsetX = sx * boardConfig.sectionWidth;
   const offsetY = sy * boardConfig.sectionHeight;
 
-  const ch: string[][] = Array(boardConfig.sectionHeight).fill(
-    Array(boardConfig.sectionWidth).fill(boardConfig.defaultCh),
+  const ch: string[][] = Array(boardConfig.sectionHeight).fill([]).map(() =>
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultCh)
   );
-  const color: string[][] = Array(boardConfig.sectionHeight).fill(
-    Array(boardConfig.sectionWidth).fill(boardConfig.defaultColor),
+  const color: string[][] = Array(boardConfig.sectionHeight).fill([]).map(() =>
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultColor)
   );
-  const bgColor: string[][] = Array(boardConfig.sectionHeight).fill(
-    Array(boardConfig.sectionWidth).fill(boardConfig.defaultBgColor),
+  const bgColor: string[][] = Array(boardConfig.sectionHeight).fill([]).map(
+    () => Array(boardConfig.sectionWidth).fill(boardConfig.defaultBgColor),
   );
-  const width: number[][] = Array(boardConfig.sectionHeight).fill(
-    Array(boardConfig.sectionWidth).fill(boardConfig.defaultWidth),
+  const width: number[][] = Array(boardConfig.sectionHeight).fill([]).map(() =>
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultWidth)
   );
 
   return { offsetX, offsetY, ch, color, bgColor, width };
@@ -44,7 +44,7 @@ export function applyChange(change: BoardChange, section: SectionData) {
 
   if (change.ch) {
     const chWidth = getCharacterWidth(change.ch);
-    const xCharacterOffset = xInSection % 2;
+    const xCharacterOffset = xInSection % chWidth;
     const offsetAdjustedXInSection = xInSection - xCharacterOffset;
     section.ch[yInSection][offsetAdjustedXInSection] = change.ch;
     section.width[yInSection][offsetAdjustedXInSection] = chWidth;
diff --git a/tests/board.test.ts b/tests/board.test.ts
index 29cd7cd..735bf32 100644
--- a/tests/board.test.ts
+++ b/tests/board.test.ts
@@ -3,7 +3,11 @@ import {
   assertEquals,
 } from "https://deno.land/std@0.224.0/assert/mod.ts";
 
-import { createBoard, renderFullBoard } from "../logic/board.ts";
+import {
+  createBoard,
+  getSectionOnBoard,
+  renderFullBoard,
+} from "../logic/board.ts";
 import type { BoardData } from "../types/board.ts";
 import { checkFullBoard } from "./checkFullBoard.ts";
 import { locateSection } from "../logic/board.ts";
@@ -14,8 +18,8 @@ Deno.test("board", async (t) => {
 
   await t.step("createBoard", () => {
     board = createBoard({
-      xSections: 2,
-      ySections: 2,
+      xSections: 3,
+      ySections: 3,
       sectionWidth: 4,
       sectionHeight: 3,
       defaultCh: " ",
@@ -24,17 +28,8 @@ Deno.test("board", async (t) => {
       defaultWidth: 1,
     });
 
-    assertEquals(board.sections.length, 2);
-    assertEquals(board.sections[0].length, 2);
-    assertEquals(board.sections[0][0].offsetX, 0);
-    assertEquals(board.sections[0][0].offsetY, 0);
-    assertEquals(board.sections[0][1].offsetX, 4);
-    assertEquals(board.sections[0][1].offsetY, 0);
-    assertEquals(board.sections[1].length, 2);
-    assertEquals(board.sections[1][0].offsetX, 0);
-    assertEquals(board.sections[1][0].offsetY, 3);
-    assertEquals(board.sections[1][1].offsetX, 4);
-    assertEquals(board.sections[1][1].offsetY, 3);
+    // Sections are created on demand.
+    assertEquals(board.sections.length, 0);
   });
 
   await t.step("locateSection", () => {
@@ -56,11 +51,12 @@ Deno.test("board", async (t) => {
     applyChangeOnBoard({ x: 4, y: 0, ch: "B" }, board);
     applyChangeOnBoard({ x: 0, y: 3, ch: "C" }, board);
     applyChangeOnBoard({ x: 4, y: 3, ch: "D" }, board);
+    applyChangeOnBoard({ x: 5, y: 3, ch: "E" }, board);
 
     assertEquals(board.sections[0][0].ch[0][0], "A");
     assertEquals(board.sections[0][1].ch[0][0], "B");
     assertEquals(board.sections[1][0].ch[0][0], "C");
-    assertEquals(board.sections[1][1].ch[0][0], "D");
+    assertEquals(board.sections[1][1].ch[0], ["D", "E", " ", " "]);
 
     applyChangeOnBoard({ x: 0, y: 1, ch: "你" }, board);
     applyChangeOnBoard({ x: 4, y: 2, ch: "好" }, board);
@@ -70,7 +66,46 @@ Deno.test("board", async (t) => {
     assertEquals(board.sections[0][0].ch[1][0], "你");
     assertEquals(board.sections[0][1].ch[2][0], "好");
     assertEquals(board.sections[1][0].ch[1][0], "嗎");
-    assertEquals(board.sections[1][1].ch[2][0], "嘛");
+    assertEquals(board.sections[1][1].ch[1], ["嘛", " ", " ", " "]);
+
+    applyChangeOnBoard({ x: 5, y: 4, ch: "啊" }, board);
+    assertEquals(board.sections[1][1].ch[1], ["啊", " ", " ", " "]);
+  });
+
+  await t.step("getSectionOnBoard: existing section", () => {
+    assert(board);
+
+    const section = getSectionOnBoard({ sx: 1, sy: 1 }, board, {
+      readOnly: true,
+    });
+    assertEquals(section.ch[0], ["D", "E", " ", " "]);
+    assertEquals(section.color[0][0], "F");
+    assertEquals(section.bgColor[0][0], "0");
+    assertEquals(section.width[0], [1, 1, 1, 1]);
+  });
+
+  await t.step("getSectionOnBoard: non-existing row", () => {
+    assert(board);
+
+    const section = getSectionOnBoard({ sx: 1, sy: 2 }, board, {
+      readOnly: true,
+    });
+    assertEquals(section.ch[0][0], " ");
+    assertEquals(section.color[0][0], "F");
+    assertEquals(section.bgColor[0][0], "0");
+    assertEquals(section.width[0][0], 1);
+  });
+
+  await t.step("getSectionOnBoard: non-existing section", () => {
+    assert(board);
+
+    const section = getSectionOnBoard({ sx: 2, sy: 1 }, board, {
+      readOnly: true,
+    });
+    assertEquals(section.ch[0][0], " ");
+    assertEquals(section.color[0][0], "F");
+    assertEquals(section.bgColor[0][0], "0");
+    assertEquals(section.width[0][0], 1);
   });
 
   await t.step("renderFullBoard", () => {
@@ -79,4 +114,11 @@ Deno.test("board", async (t) => {
     const rendered = renderFullBoard(board);
     checkFullBoard(rendered);
   });
+
+  await t.step("on-demand creation: only changed sections are saved", () => {
+    assert(board);
+
+    assertEquals(board.sections[2], undefined);
+    assertEquals(board.sections[0][2], undefined);
+  });
 });
diff --git a/tests/character.test.ts b/tests/character.test.ts
index 886d7ad..c8e3a65 100644
--- a/tests/character.test.ts
+++ b/tests/character.test.ts
@@ -26,14 +26,18 @@ Deno.test("getCharacterWidth CJK", () => {
   assertEquals(getCharacterWidth("グ"), 2);
   assertEquals(getCharacterWidth("ソ"), 2);
 
-  assertThrows(() => getCharacterWidth("？"));
-  assertThrows(() => getCharacterWidth("！"));
+  assertEquals(getCharacterWidth("？"), 2);
+  assertEquals(getCharacterWidth("！"), 2);
   assertThrows(() => getCharacterWidth("你好"));
   assertThrows(() => getCharacterWidth("ヨスガノ"));
 });
 
+Deno.test("getCharacterWidth Emoji", () => {
+  assertEquals(getCharacterWidth("👋"), 2);
+  assertEquals(getCharacterWidth("🌲️"), 2);
+  assertEquals(getCharacterWidth("👨‍👩‍👧‍👦"), 2);
+});
+
 Deno.test("getCharacterWidth previously faulty cases", () => {
   assertEquals(getCharacterWidth("𤲶"), 2);
-
-  assertThrows(() => getCharacterWidth("𤲶"[0]));
 });
diff --git a/tests/checkFullBoard.ts b/tests/checkFullBoard.ts
index 9984249..9484c40 100644
--- a/tests/checkFullBoard.ts
+++ b/tests/checkFullBoard.ts
@@ -47,6 +47,11 @@ export function checkFullBoard(board: FullBoard) {
       console.error("width:   ", widthLine);
     };
 
+    if (typeof cCh !== "string") {
+      printSituation();
+      throw new Error("cCh is not string");
+    }
+
     if (!isValidColor(cCo) || !isValidColor(cBg)) {
       printSituation();
       throw new Error("cCo or cBg is not valid");
diff --git a/tests/section.test.ts b/tests/section.test.ts
index 8a5a139..a70da5b 100644
--- a/tests/section.test.ts
+++ b/tests/section.test.ts
@@ -90,27 +90,33 @@ Deno.test("section", async (t) => {
     assert(section);
 
     applyChange({ x: 0, y: 0, ch: "t" }, section);
-    assertEquals(section.ch[0][0], "t");
-    assertEquals(section.ch[0][1], " ");
-    assertEquals(section.width[0][0], 1);
+    assertEquals(section.ch[0], ["t", " ", " ", " "]);
+    assertEquals(section.ch[1], [" ", " ", " ", " "]);
+    assertEquals(section.width[0], [1, 1, 1, 1]);
+  });
+
+  await t.step("applyChange 1-width at odd position", () => {
+    assert(section);
+
+    applyChange({ x: 1, y: 0, ch: "t" }, section);
+    assertEquals(section.ch[0], ["t", "t", " ", " "]);
+    assertEquals(section.width[0], [1, 1, 1, 1]);
   });
 
   await t.step("applyChange 2-width at a correct position", () => {
     assert(section);
 
     applyChange({ x: 0, y: 0, ch: "あ" }, section);
-    assertEquals(section.ch[0][0], "あ");
-    assertEquals(section.ch[0][1], " ");
-    assertEquals(section.width[0][0], 2);
+    assertEquals(section.ch[0], ["あ", "t", " ", " "]);
+    assertEquals(section.width[0], [2, 1, 1, 1]);
   });
 
   await t.step("applyChange 2-width at an alternate position", () => {
     assert(section);
 
     applyChange({ x: 1, y: 0, ch: "あ" }, section);
-    assertEquals(section.ch[0][0], "あ");
-    assertEquals(section.ch[0][1], " ");
-    assertEquals(section.width[0][0], 2);
+    assertEquals(section.ch[0], ["あ", "t", " ", " "]);
+    assertEquals(section.width[0], [2, 1, 1, 1]);
   });
 
   await t.step("applyChange incorrect section", () => {