是非とも・是非共|ぜひともzehitomo[1]atamadaka (head-high)

1. adverbby all means; at all costs; absolutely
   あなたの迅速じんそくな返事へんじが是非ぜひとも必要ひつようです。↗

   Your prompt reply is urgently required.

• Synonym絶対にぜったいにNeutralNot a true antonym: it can also mean 'by all means', as in 「絶対に来てね」; mostly for firm assertions, while 「是非とも」 centers on requests and wishes.
• Synonym必ずかならずNeutralNot a true antonym either: it can appear in requests, as in 「必ず来てください」; it stresses that something will certainly be done, 「是非とも」 an earnest wish.
• Synonym是非ぜひNeutralSlightly lighter in tone than 「是非とも」 and very common in speech; also a noun meaning right and wrong.
• Synonym何卒なにとぞFormalA formal way of entreating someone, mostly in letters and speeches; 「是非とも」 can also voice one's own strong wish.
• SynonymどうしてもNeutralUsed for doing something no matter what, and with a negative for when something just won't work; 「是非とも」 is mostly for requests, wishes or resolve.
• SynonymぜひぜひCasualA colloquial doubling for urging or inviting warmly, as in 「是非是非来て」; 「是非とも」 leans formal.
• Synonym何が何でもなにがなんでもNeutralAn idiom for getting something done at any cost, stressing resolve; harder-edged than 「是非とも」 and rarely used in requests.
• RelatedどうぞNeutralA gentle 'please' for offering something or giving permission; 「是非とも」 is a strong, earnest request.
• Related理が非でもりがひでもWrittenAn idiom for seeing something through right or wrong, with a forceful, by-any-means tinge; 「是非とも」 carries no such nuance.
• Related雨が降ろうと槍が降ろうとあめがふろうとやりがふろうとNeutralAn idiom for pressing ahead come what may, stressing resolve in an exaggerated tone; it can also introduce a request, but 「是非とも」 has no such hyperbole.

Use 「是非とも」 for a strong wish or a formal request, as in 「是非ともお越しください」. In casual speech say 「ぜひ」; for earnest entreaty in letters or speeches, 「何卒」; when you'll do something no matter what, 「何が何でも」; for plain certainty, 「必ず」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. なにがなんでも。きっと。是非ぜひ。