Mukuro never knew why he came to respect Tsuna.
Why he would grow an attachment to the Vongola Boss. He hated the mafia; he tried to take over it. When he finally though he could defeat the last boss in line of the Vongola family and lost he started to doubt. The short second they clashed, he saw those eyes, eyes impossible of betrayal. As he was dragged back by Vindicare he heard him asking why he must be imprisoned. He wasn't surprised why Reborn told him Tsuna cared for his wellbeing, and when he was asked to join the family, he agreed at once in his head. He never regretted saying 'yes' to Reborn.
Even during the future, as he was losing to Byakuran he remembered the brown-ember eyes, that never failed to mesmerise him. He wondered how he came to trust those eyes, to join the mafia whom he hated, to always put down his pride and lose Kyoya to stop the fight so Tsuna wouldn't be worried. He wondered when he considered Tsuna as a friend, someone to trust, and someone he would protect. Was it Chrome? Did her affection to his kindness affect him as well? Tsuna was too innocent, pure and right to be a mafia boss.
When he got his future memories after the great battle, he saw the will of his Boss, yes, HIS boss. He could only laugh in his head and congratulated Chrome in her efforts in her head without forgetting to add the normal kufufu after the sentence.
As he lost contact with Chrome during their voyage for the Shimon, he was worried, his heart tensed, and in his cold, watery grave he panicked. Mukuro, as he possessed Chrome he did it for Tsuna, knowing he would want him to come, when his body was taken, he even used his last strength to possess the stupid owl.
He held no ill will as Tsuna gave a sickening punch to his body, he held no ill will that his body was crumbling to pieces, and he even cracked a sick joke that he'll be fine.
He regretted being an ally to Verde, he regretted attacking Tsuna even as he kept his mask of hating the mafia, he could see worry in Tsuna's eyes. He knew attacking him was against his will, but he played along never the less, to defeat him and protect his family from Colonello's soon to come attack.
His heart swelled with joy as Byakuran protected Tsuna from the attack, all hatred for him disappeared and he wondered when he became forgiving.
Tsuna was a man who had power yet held the innocence no mafia boss in his generation had. Mukuro held respect for him and in his heart there was a place for him, he knew Tsuna still cared for him and that was all Mukuro needed. A place to belong, he found it in Tsuna.
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