The shortest, most natural way to say “back to life” in Japanese is: 生き返る（いきかえる） — ikikaeru
This is a single verb meaning “to revive,” “to come back to life,” or “to be restored to life.”

Other short options (depending on context)

1. Literal “return to life”

  • 回生（かいせい） — kaisei
    A noun meaning “resurrection” or “coming back to life.” Often used in phrases like kaisei suru (to resurrect).

2. Idiomatic “revive from death”

  • 起死回生（きしかいせい） — kishi kaisei
    A four-character idiom (yojijukugo) meaning “to rise from death and return to life,” often used metaphorically for turning around a hopeless situation.

3. More literal phrasing

  • 人生に戻る（じんせいにもどる） — jinsei ni modoru
    “Return to life” in the sense of returning to one’s life (e.g., after an absence), not necessarily resurrection.

Quick usage notes

  • 生き返る is the most direct and shortest way if you mean “come back to life” (e.g., after death or extreme exhaustion).
  • 回生 is more formal/literary, often used in medical or religious contexts.
  • 起死回生 is best for dramatic or metaphorical revival (e.g., a sports team making an impossible comeback).

Example sentence

The rain brought the plants back to life.
雨が降って草木が 生き返る 。
Ame ga futte kusaki ga ikikaeru.

TL;DR

  • Shortest : 生き返る（いきかえる）
  • Formal/literary : 回生（かいせい）
  • Idiomatic/dramatic : 起死回生（きしかいせい）

Information gathered from public forums or data available on the internet and portrayed here.