Background Effects

In manga and anime, kouka-haikei 効果背景, "effect backgrounds," are backgrounds which express some sort of effect, like representing the emotion that a character is feeling.

Anime: Bakuman. バクマン。 (Episode 4)

• Types
  
  • Speed Lines
  • Focus Lines
  • Radiated Lines
  • Uneasy Lines
  • Ropes
  • Dripping Blue Lines
  • Beta Flash
  • Lightning
  • Soap Bubbles
  • Lilies
• Techniques
  
  • Stippling
  • Hatching
  • Halftoning
    
    • AM Halftone
    • FM Halftone
  • Screentoning

Types

For reference, a list of various types of background effects.

Note that, among them, the ones that are rendered using only lines are also called "effect lines," kouka-sen 効果線.

Speed Lines

The "speed lines," supiido-sen スピード線, are parallel lines drawn across the background to represent the tremendous speed or characters or objects, making them one type of motion lines.

Manga: One Punch Man (Chapter 10)

• hayai!
  速い！
  [He] is fast!

These lines also have a different use: sometimes they're drawn vertically, going up, even though characters are standing still. In this case, they represent a surge of emotion, excitement, anger, or other sort of fervor.

Anime: Mahoujin Guruguru 魔法陣グルグル (2017) (Episode 1)

Focus Lines

Lines drawn from the edges of a panel in manga or from the edges of the screen in anime and going toward the center or to a focal point are called "focus lines," shuuchuu-sen 集中線.

They're used in various ways, including to emphasize a focused element:

Manga: Boku no Hero Academia, 僕のヒーローアカデミア (Chapter 48)

• Context: Midoriya Izuku 緑谷出久 realizes something about himself.
• kono taiyaki ga boku'...desu!!
  このたい焼きが僕っ･･･です！！
  This taiyaki... is me!!
  • taiyaki たい焼き
    A sort of fish-shaped pancake.

Or when a character is focused, concentrated, and about to use a skill:

Manga: Naruto ナルト (Chapter 41, 悪魔の囁き･･･！？)

• Context: a ninja activates their special eyes.
• byakugan!!
  百眼！！
  White eyes!!

Radiated Lines

When lines are drawn radiating from a character, that means the character is cheerful, is happy.

Manga: One Piece (Chapter 9, 〝魔性の女〟)

• Context: Nami ナミ cheers up.
• honto!?
  ほんと！？
  Really!?
  • hontou 本当 with the long vowel shortened.

Uneasy Lines

When lines are drawn curved like tentacles reaching out to a character or place, that means the place is creepy, the atmosphere feels weird, bizarre, the character feels uneasy, anxious, or angry.

These are called odoro おどろ, by the way.

Manga: Mob Psycho 100, Mobu Saiko Hyaku モブサイコ１００ (Chapter 55, 知らない)

Ropes

In manga, when a pattern that looks like ropes is drawn in the background of a panel, that generally means the character is worried or anxious.

These are called nawaami ナワアミ, by the way.

Manga: Black Jack, ブラック・ジャック (Chapter 1, 報復)

• ...okuyami wo tsutaete kudasai
  ･･･おくやみをつたえてください
  ...communicate my condolences.
• makoto ni zan'nen desu to
  まことに残念ですと････････････
  [Say] that [it was] truly unfortunate............
  [Say] that [I'm terribly sorry for what happened]............

Dripping Blue Lines

The "dripping lines," tare-sen タレ線, are vertical lines drawn dripping from the top of the panel, used when a character feels down, depressed, or shocked, among other uses.

They're typically rendered as blue lines in anime and colored manga.

Anime: Bokutachi wa Benkyou ga Dekinai ぼくたちは勉強ができない (Episode 1)

Beta Flash

The "beta flash," or betafura ベタフラ, is a white flash of light drawn on a background "filled with the black color," beta ベタ.

It's used when a character notices, realizes or deduces something.

Manga: Assassination Classroom, Ansatsu Kyoushitsu 暗殺教室 (Chapter 1, 暗殺の時間)

• nyari
  ニャリ
  *grin*
  

Lightning

A lightning background is used when a characters feels shocked, when something shocking happens or when they come to a shocking realization.

Anime: Ore wo Suki nano wa Omae dake kayo 俺を好きなのはお前だけかよ (Episode 2)

Soap Bubbles

A background featuring "soap bubbles," shabon-dama シャボン玉, or other light shapes, is typically used for a soothing, calming, endearing, or romantic effect.

Manga: Aho Girl, Aho Gāru アホガール (Volume 1, Chapter 3, Page 26)

• Context: Akkun あっくん, who doesn't have friends, makes his first friends.
• genki...... dashite kudasai ne?
  元気･･････出して下さいね？
  [Cheer up,] okay?
• yoshi yoshi
  よしよし
  [There there].
• yokatta nee Akkun
  よかったねーあっくん
  [Isn't that great,] Akkun.
• nadenade
  なでなで
  *pat pat*
  • Reduplication of:
  • naderu
    撫でる
    To pat. To caress.
• ...yasashisa ga tsurai...
  ･･･優しさがつらい･･･
  ...kindness [hurts]...

Lilies

Sometimes, lilies in the background of a scene featuring girl on girl romance is a visual pun on a Japanese term for lesbian fiction: yuri 百合, which means literally "lily," the flower.

Anime: Ouran High School Host Club, Ouran Koukou Hosuto-Bu 桜蘭高校ホスト部 (Episode 9)

Techniques

Besides the background effects listed above, here are some terms for techniques and patterns typically used in backgrounds.

Stippling

In art, "stippling," or tenbyou 点描, is the use of dots to shade an area. In manga, stippling isn't a very common technique, but it's sometimes used to shade light areas, like sand and soap bubbles.

Manga: Black Jack, ブラック・ジャック (Chapter 2, シャチの歌)

Hatching

In art, hatching is the use of lines to shade an area. Cross-hatching is the use of lines that cross each other.

In manga, kakeami カケアミ is the term for a common hatching pattern in which lines are drawn in bundles, like scratches, and the bundles don't cross each other, but the lines within a bundle may cross each other.

Manga: Bokura wa Minna Kawai-sou 僕らはみんな河合荘 (Chapter 2)

In some cases, the bundles are outlined, turning into overlapped rectangles.

Manga: AQUA (Chapter 5, 希望の丘)

Halftoning

Halftone is a printing technique to render tones by using a pattern of dots with varying sizes and spacing. There are actually two types of halftones, and both are used in manga.

AM Halftone

The term amiten 網点, "dot net," refers to amplitude-modulated halftone. They look like a net, a grid made out of dots, points. At certain densities, it looks like a polka dots pattern.

Manga: Gabriel DropOut, ガヴリールドロップアウト (Chapter 5)

• Context: Vignette ヴィネット just wants to get with the program.
• maa ii wa...
  まぁいいわ･･･
  Whatever... (never mind that.)
• hajimemashou
  始めましょう
  Let's start. (already.)

Often this halftone is too small for the pattern to be discernible.

Manga: Yuru Yuri ゆるゆり (Volume 1)

FM Halftone

The term suname 砂目, "sand grain," refers to the frequency-modulated halftone. It's a random noise often used to render gradients, though it can also be used on grainy textures.

Manga: Houshin Engi 封神演義 (Chapter 1, 封神の書)

Screentoning

A "screentone," sukuriin-toon スクリーントーン, is a semitransparent sheet of paper with one or more patterns or textures printed on it. Artists slice out pieces of the screentone in the shape of the areas that they want to apply the pattern to, and then paste it onto the drawing.

Anime: Bakuman. バクマン。 (Episode 4)

Most background effects you see in manga come from screentones, including the amiten, suname, and kakeami patterns, among others, like parallel strips, soap bubble patterns, flower patterns, and so on.

Furthermore, nowadays there are also digital artists who use digital software that can apply textures like these digitally.