There are many KANJIs made with KOKORO radical. Among them, I would like to introduce a KANJI character "忍:NIN/SHINO(BU)".
You will find this character as "刃" on "心".
"刃" means edge while "刀" means blade.
TOU/KATANA
HA/YAIBA
Getting them together, "忍" means a hidden intention. And a person with hidden intention will be called as "忍者:NINJA".
Then "忍" is also used in "認", meaning recognize or authorize because the radical "言:GEN/I(U);say"(GONBEN) is used for things related to saying something.