Both Sasuke and Madara's Sharingan awakened/evolved after they

What If Itachi Got The Eternal Mangekyo Sharingan In Naruto?

naruto - Did the writer mention that 2 Tomoe Sharingan can instantly awaken into Mangekyou Sharingan? - Anime & Manga Stack Exchange

Both Sasuke and Madara's Sharingan awakened/evolved after they broke their bond with their best friends. I love this parallel. : r/Naruto

How did Sasuke get the Rinnegan? Here's what you should know

Evolution of the Sharingan and Other Eyes: Naruto Shippuuden

Evolution of the Sharingan and Other Eyes: Naruto Shippuuden

Who has the Eternal Mangekyo Sharingan?

Madara Teaches Sasuke how to use sharingan

How did Sasuke and Madara ever exist at the same time since they were both reincarnation of Indra? Did Madara still have his soul? - Quora

Mangekyou Sharingan