それがやれるのは今だけだ。

that (indicating an item or person near the listener, the action of the listener, or something on their mind); it; that time; then; there (indicating a place near the listener); you

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

now; the present time; just now; soon; immediately; (one) more

only; just; merely; simply; no more than; nothing but; alone; as (e.g. as soon as, as much as); worth

be; is; indicates past or completed action; indicates light imperative