What is first legal requirement for formation of a company? This is willingness to form a company. Who should have this willingness? The promoter! Who will be the promoter? Any person, natural or legal! However, in case of One Person Company only a natural person can incorporate a company. Even in case a legal person, a natural person shall digitally and manually sign the incorporation forms and documents.
This is needless to say even a form for reservation of a name for proposed company need a digital signature among other requirements.