The first edition Shadowless Pokemon cards were bought directly from original US publishers Wizards Of The Coast in 1999.
And now the set – protected in plastic sleeves and in excellent condition – will be sold by an auction house in Lichfield next week.
The 102-card shadowless set actually features 103 cards – with two different versions of Pikachu, numbered 58a for Red Cheek Pikachu and 58b for Yellow Cheek Pikachu, made.
It also comes with a vintage 1990s official Pokemon trading card binder with the slogan "Gotta catch 'em all" on the cover of it.
The cards were printed before the redesign that added the shadow, which means they are older and more valuable, hence the "shadowless" name.
The collection is expected to fetch between £25,000 to £35,000 when it goes under the hammer by Richard Winterton Auctioneers.
Nigel Brookes, who is selling the cards, received the collection for his 14th birthday in 1999 – with it put safely aside as the value grew.
Mr Brookes, from Streetly in Birmingham, decided now was the time to give another enthusiast the chance to enjoy it.
And the father-of-three hopes the money will benefit his children as they grow up – with his eight-year-old daughter Layla even offering £6 for it.
The 33-year-old said: "It soon became apparent that this collection could become an ace up the sleeve one day.
"We’ve looked after this for 20 years and hope it will go to someone who will respect it in the same way."
The Pokemon Trading Card Game – based on the Nintendo franchise – was released in October 1996 by Media Factory in Japan and by Wizards Of The Coast in the US.
Jon Price, from Richard Winterton Auctioneers, said: "This a very rare chance to buy a first edition set of the Shadowless Pokemon trading cards.
"They do not come up very often and this one is particularly special because it has been in the same family from new and carefully kept safe for more than 20 years."
The sale will be carried out by the auction house at 4pm on July 27 through The Saleroom and Easy Live Auction – with the time chosen to accommodate international buyers.
Viewing in person is carried out through an appointment basis – with people asked to call 1543 251 081 or email firstname.lastname@example.org