@BraegenE943 if you read this, it means that I kinda of have an original idea so after Kir Transport Case, the mystery person (original character) have the same ability like Kuuga and his personality is like Udō Jin-e from Ruroini kenshin
And he was searching for the famous assassin and a swordmans name BLADE(Kuuga), who was obsessed of wanted to defeat BLADE, for enjoyment and killing.
He found BLADE location and he didn't matter and doesn't care, if BLADE turn into a child and have a name called Kuuga, he only wanted BLADE to fight in his Prime/fullest potential, but after seeing BLADE(Kuuga) helping his adoptive father and friends.
He leaves, and state if BLADE(Kuuga) cannot fight him to his fullest potential, then Kuuga have no absolute chance of winning. Then at Night he end up kidnapping Haibara Ai in effort to coerce Kuuga into becoming a ruthless assassin BLADE once again, and fight BLADE(Kuuga) in a battle to the death.
Also the fight between Kuuga and (original character name) is the fight like Kenshin vs Udō Jin-e and some mix of Robin(Damian Wayne) Vs Deathstroke from the movie called
Son of Batman(2014).
So what do you think of my idea and I have no idea of come up, thr name of the original character, that Kuuga fight
The original character have the same personality of Udō Jin-e