Actually i based my 'opinion' on the manga. Tbh i wouldnt even call it my opinion because the manga has made it very clear already that it didnt need senju dna, its you people didnt understand what tobi meant.
Kishi hasnt contracted himself at all because tobi said he boasted a complete izanagi unlike danzo. From what ive gathered, hashirama dna gives the sharingan abilities a boast. This is the reduction time for ka for example.
An uchiha can use the technique without senju dna, but theirs would be incomplete because they are just uchiha's.
When a non uchiha with the sharingan is to use the technique they would need to boost their energy and we danzo did this, but his was also incomplete because although he might have senju dna, he isnt an uchiha.
Tobi is the only person who boasts a complete izanagi and he said its the combination of both uchiha and senju that allows his to use the complete form. This is also why i believe tobi is an uchiha
So basically true uchiha's = incomplete
Non uchiha's with hashirama dna = incomplete
True uchiha + hashirama dna = complete
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