はAs for... (Highlights sentence topic)

The particle の often shows possession, like the English ''s' (e.g., ケンジの本 means 'Kenji's book'). It can also connect two nouns, as in 日本人の学生 ('a student who is Japanese'). In contrast, は marks the topic of the sentence. Unlike の, it doesn't show possession — it introduces what the rest of the sentence will describe or explain.

When は follows a number or amount, it often adds a contrastive nuance like 'at least' or 'no more than.' For example, １回は行ったけど means 'I went once, but no more than that.' This is similar to contrastive uses of は, like in 田中さんは行ったけど ('Tanaka went, but no one else did'). If there's no contrast, the number is usually used without a particle, as in 三つ買った ('I bought three').

Both といえば and は can introduce the topic of a sentence. といえば is used when referencing something previously mentioned or known, often implying that more information will follow ('speaking of…'). は is broader and can also suggest contrast, as in 'バナナは食べたけど…' ('I ate the banana, but [not the apple]'). といえば doesn't create contrast in this way.

って is used in casual conversation to introduce a topic informally. It comes from the quotation particle と and can carry the nuance of 'speaking of…'. は is a more standard and flexible topic marker, used in both casual and formal situations, including writing. Unlike って, は can also carry a contrastive nuance.

The particle は marks the topic of a sentence, or what the sentence is about. が usually marks the grammatical subject, especially when introducing new information or expressing desire, ability, or necessity. は can also show contrast, while が emphasizes what it marks.