The evil Uchiha brat actually seduced my brother?!

incurable disease...

After Madara had just been discharged from the hospital, he bumped into Hashirama. Madara looked at him with a frown, but Hashirama seemed relieved to see that Madara was okay.

However, Madara seemed indifferent to whether Hashirama was worried about him and said impatiently, 'What are you here for?'

Hashirama said, 'This is for you:' but Madara directly refused, saying, 'Isn't this something you said you wanted to give to your future wife when you were young? Why are you giving it to me?' Hashirama replied:'It's nothing. I have other gifts.'
'Thanks' replied Madara

Madara directly ignored Hashirama and walked away.

Madara went home, opened the abortion pills, and swallowed them all at once. A moment later.....he was in excruciating pain, which brought him to tears. Then he felt nauseous and, standing by the toilet, began to vomit.

Suddenly, the gift Hashirama gave him, a pendant, began to emit a series of bright flashes.

Madara suddenly realized that the child in his womb was absorbing the chakra from the pendant. Specifically, it was Hashirama's yang chakra. Since Madara's body lacked yang chakra, the child only had yin chakra. Therefore, if Madara wanted to keep the child, he needed Hashirama's yang chakra.

Madara:...

So, Madara conspired with the doctor to deceive Hashirama. First, Madara approached Hashirama and spoke about his 'terminal illness,' using it as a pretext to extract chakra from him. Once the child was born, Madara planned to fake his own death under the guise of the illness.

The plan was successful. Although Hashirama was somewhat skeptical, he still respected Madara. Thanks to Madara's careful acting, Hashirama, despite appearing sad and dejected, continued to regularly provide him with chakra, all in the hope of prolonging Madara's life, as he believed Madara was suffering from a terminal illness.

(Hashirama haven't discovered his feelings for Madara)

Soon Hashirama got married....

8 months later...
The son of Madara is born
Madara named him uchiha obito

Madara's son, Obito, was born. So, Madara's next plan was to raise Obito until he turned 12 and then orchestrate an accident.
(Everyone thought madara died)

Although he was as foolish as Hashirama, because Obito's ideals were very naive. But he's still very skilled. Obito also inherited Hashirama's Wood Release kekkei genkai. But madara doesn't allow him to use it because they would get caught.