shall be leader

[keannu]

This "shall" in "shall be leader" seems to be a rare usage. Does it mean "willingness"? Is it common?

310-299
ex)"Who will lead the exercises today?" the teacher asked. No one answered. The teacher laughed. "Very well. Then I shall be leader." The teacher kicked off her shoes and the girls laughed...

[SoothingDave]

"Shall" is becoming archaic.

"I will" implies a sense of purpose or determination.

"I shall" simply states the fact.

Shall | Define Shall at Dictionary.com

The rule continues that to express determination,

will is used in thefirst person ( We will win the battle ) and shall in the other two persons( You shall not bully us. They shall not pass ). Whether this rule wasever widely observed is doubtful. Today, will is used overwhelminglyin all three persons and in all types of speech and writing both for thesimple future and to express determination. Shall has some use in allpersons, chiefly in formal writing or speaking, to expressdetermination: I shall return. We shall overcome. Shall also occurs inthe language of laws and directives: All visitors shall observe postedregulations. Most educated native users of American English do notfollow the textbook rule in making a choice between shall and will. Seealso should.

[5jj]

"Shall" is becoming archaic.

It is indeed, but you'll still hear it from older Brits - including me.

[SoothingDave]

It is indeed, but you'll still hear it from older Brits - including me.

And it's heard in certain stock phrases, like "shall we go?"

[5jj]

And it's heard in certain stock phrases, like "shall we go?"

I wouldn't call 'shall we go' a stock phrase. 'Shall we ...' is a fairly common way of introducing a suggestion in BrE.