Contrary to common belief, the Kodokan emblem is not a cherry blossom, but rather a representation of a mythical 8 sided mirror given to the first emperor of Japan by the Gods, as the legend goes.
From the Kodokan:
http://kodokanjudoinstitute.org/en/beginner/about/
What images was the Kodokan symbol derived from?
The
red circle expresses an iron-core that is fired, and the white outward
means the floss silk that wraps the core. The floss silk is pure white
and has toughness although it is soft. The more one forges iron, the
more it becomes strong.
The symbol expresses the idea that
Kodokan members should always have the following spirit: Soft-outward
and hard-inward. That is to say, they should have a mighty heart and
strengthened physical ability while they behave softly, calmly and
rightly to others.
The symbol was made in 1940 improving a symbol
that was set by Kano Shihan in the early days of Kodokan. It expresses
the spirit of soft-outward and hard-inward. The flower-shaped outward
expresses a flower shaped mirror that means trainees should have always
Shihan's words in their mind.
From Judoinfo:
http://judoinfo.com/kdk.htm
Although this is the most
widely-publicized interpretation of the Kodokan symbol in the west, it
is not the most accurate account. A cherry blossom (sakurabana) in
Japanese crests is always represented with five petals, as shown in this
symbol and photo of a cherry blossom. By contrast, the Kodokan emblem
has eight pointed lobes. Some judo clubs and organisations have used the
five-lobed cherry as part of their emblems, and as a meaningful Samurai
symbol it is also accepted. But the Kodokan symbol has different
origins. The colors in the symbol worn by members of the Kodokan
represents a piece of red hot iron surrounded by pure white floss silk
-- hard in the centre, soft on the outside. The badge emphasizes the
judo principle that the soft controls the hard, or gentleness can
control force, that one can win by using the opponent's force against
himself.
The Kodokan symbol was not used until after Jigoro Kano
died, so he may not have been involved in selecting it. A small pamphlet
purportedly published by the Kodokan explained that the current Kodokan
symbol was introduced in October 1940, and that the form is modeled
after an ancient 8-sided copper mirror (called yata-no-kagami). This
mirror is chronicled in Japanese Shinto legends and the shape is
represented in numerous Japanese crests (mon). The mirror, reflecting
everything truthfully, is a symbol for honesty. The red circle in the
center was intended to symbolize a sincere and passionate mind. This
historical account is now accepted as the authentic origin of the
Kodokan symbol, and it has been confirmed by the Kodokan (Naoki Murata,
director of the Kodokan Museum).
The Kodokan symbol is the
representation of Yata no Kagami, or "The Mirror Yata" or "The Octagonal
Mirror". According to the mythical history of Japan, the Gods offered
three sacred gifts to the first japanese emperor to prove his "divine
descendence":
KUSANAGI NO TSURUGI - "The Sword Kusanagi"
YASAKANI NO MAGATAMA - "The Jewel Yasakani"
YATA NO KAGAMI - "The Mirror Yata"
The
Yata no Kagami is not a normal mirror. Unlike normal mirrors that
reflect our external image, Yata no Kagami reflects our soul. For this
reason, there are always mirrors inside Shinto temples (it is said the
original Yata no Kagame still remains untouched inside a Shinto temple
in Japan). Applying Shinto concepts in the symbol of Judo, the white
color of Yata no Kagami represents the Judoka's search for purifying
his/her soul, and the red sun in the middle stands for the virtues of
Judo which the Judoka should focus on..