I've done some research from the Steam discussions and the wikia.
Some discussions say that Leo is a girl because:
1. Eleonor is a girl's name.
2. He/she has a bikini suit TEKKEN Tag Tournament 2.
3. Harada himself said that Leo is a girl.
4. Leo can equip pigtails in TEKKEN 6 which is only for females.
5. Even though, Yoshimitsu referred Leo as a "he" in the TEKKEN 7 Story Mode. Yoshimitsu said that Leo is a "charming yet delicate" martial-artist, and you know
what I mean by that.
6. If you play as Yoshimitsu in TEKKEN 7 Story Mode. Yoshimitsu will said "Such a beautiful opponent" to Leo in the intro before the battle.
8. Leo has a tracksuit top in TEKKEN 7 which is for female.
But part of the community refers Leo as a boy because:
1. He/she oftenly referred as a "he" in the game
2. In the TEKKEN 6 artbook (if you have one). Leo is in the male characters section.
3. Leo can equip a sledgehammer in TEKKEN 6 which is only for
males.
4.Yoshimitsu referred Leo as a "he" in the TEKKEN 7 Story Mode.
5. The name's Leo is oftenly used for a boy's name.
6. Even though Leo was in the TEKKEN Girls group, he/she was removed when TEKKEN 7 came out.
7. Leo has a facial hair items in TEKKEN 7 which is only for males.
8. Leo's German voice sounded more masculine with a deeper pitch that enhance the theory about Leo being a boy.
There are some people said that Leo in TEKKEN 6, TEKKEN Tag Tournament 2, and in TEKKEN 7 is a different person. Those people think that Leo is a name for 3 different people or maybe twins who fight in different games. But, no in-game proof that proofs if Leo in TEKKEN 6, TTT2, and TEKKEN 7 are different person. And there are no developer's statement that they can use as a base for the theory.
Even the TEKKEN WIKIA itself stated that Leo's gender is ambiguous.
Leo's weight or mass is also unknown, which is also crucial about determining Leo's gender.
Extra
Note:
1.Leo's battle voice in every TEKKEN game and dialogue voice in TEKKEN 6 is voiced by Veronica Taylor who voices Ash Ketchum in Pokémon animated series.
2.Meanwhile, Leo's German voice actor in TEKKEN 7 and TEKKEN Tag Tournament 2 is still unknown.
This post was ultimately source from the TEKKEN WIKIA (55%) and from my experience playing TEKKEN (45%)
Now, what is your argument about Leo's gender?
(Sorry for its writing that is too long)
Yeah, TEKKEN's cool!!
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