godan verb (-ru), intransitive verb
steal into; sneak into; slip into
Describes entering a place quietly and secretly, often with a nuance of stealth or illicit intent. Used for physical intrusion.
夜中に泥棒が家に忍び入った。
A burglar sneaked into the house in the middle of the night.
彼は誰にも気づか
He slipped into the room without anyone noticing.