ともEven if, No matter

にしても and とも both express 'even if', but differ in formality and structure. にしても follows the plain, non-past form and is more common in daily language, e.g. どこに行くにしても ('No matter where you go'). とも follows the volitional form and is more formal and emphatic, often found in set expressions like 何があろうとも ('No matter what happens').

Both express strong contrary hypotheticals, similar to 'Even if (A), still (B)'. たとえ〜ても is less formal and more common in speech, e.g. たとえ一人でも、ちゃんとやる 'Even if it's just me, I'll do it right.' とも is more literary and formal, and takes the volitional form, e.g. 死のうとも構わない 'Even if I die, I don't mind.'

どうしても and とも both express the meaning of 'even if' or 'no matter', but differ in formality and placement. どうしても comes at the beginning of a sentence to emphasize determination, as in どうしても勝ちたい ('I want to win no matter what'). とも is a verb ending, often more formal or literary than ても. For example, 彼女が何と言おうとも ('No matter what she says') is equivalent in meaning to 彼女が何と言っても, but more formal.

Both mean even if or no matter if. とも states a single condition in a slightly formal style, as in 雨が降ろうとも行く (I’ll go even if it rains). ようが～まいが is more emphatic, presenting contrasting alternatives, as in 雨が降ろうが降るまいが行く (I’ll go whether it rains or not).