Often we can feel a little lost and overwhelmed when choosing a new Koi. Predicting how a Koi will develop in the future requires a great deal of understanding,... and every bit of insight helps.
In this pic we see 4 tosai Showas - they are all siblings (from the same Mother, and likely from the same Father) - notice the similarities,... body shape, face shape, shoulder marking, sumi, and red brick tint of Hi - the interesting thing here is the 1st Showa on the left was born here in '01,... and the other 3 were born here in '03 - they are all siblings, but separated by 2 years. Though they are separated by 2 years the genetics are the same, and the older sibling CAN be used to give us an "idea" of how these 2nd, 3rd, and 4th Showas will develop in the future.
If older siblings are available, look them over to get a better understanding of what you will likely have from your fish in the future. This is a photo of Showa tosai #1 as it looks now - we can expect similar development from the other three younger siblings down the road. Older siblings can take a lot of the guesswork out of a new Koi purchase.

Best Wishes,
Brady Brandwood