Because at some point in his life, Tsuna knew he acknowledged him as his biological father. I do not own Katekyo Hitman Reborn.
Tsuna was supposed to be dead,but fate has another plan for him. Waking up into a parallel world where everything is the same as his old one but yet different. For instance, he was not the Vongola candidate whereas his older twin brother Natsume is. And somehow,his reputation in Namimori is horrible and everyone hates...
"Re-Rene-san...?" The said brunet turned his head slightly, arms propped over his knees as he sat down next to the younger. The adult's tattered fedora shadowed his brown eyes as he gazed at the child. "Mm? What is it, Izuku-kun?" The green-haired child rubbed at his puffy eyes feverishly, looking up with teary iris...