すぐに返事を書いてください。

immediately; at once; directly; soon; before long; shortly; easily; without difficulty; right (near); nearby; just (handy)

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

reply; answer; response

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to write; to compose; to pen; to draw; to paint

to give; to confer; to bestow; to kindly do for one; to oblige; to favour; to favor