Actually, after Tsuna asked Kyoko and was rejected by her. Haru came in and conforted him, in the process, Tsuna would have told Haru about his dark past something that only Gokudera, Yamamoto and Haru knows. Haru would have listened to him, crying with him, and feeling his pain. Tsuna asked her to stay quiet about this, Haru have promised to not say a word about it. The kindness that Haru showed that day to Tsuna, made him begin to have feeling for her or to have awkened feelings that were here from long time ago.
From that event, Tsuna began to see Haru somehow more beautiful than before, something that he didn't understood. Of course following, Kyoko's rejection he was really sad but deep inside him he knew that Kyoko never loved him yet he believed in this fake, one-sided love. What did hurt him the most was that he knew this fact for long. Haru came everyday at his house to confort him, and surprisingly he was glad she was here, always resting on her lap, feeling peaceful with her here. After a period, he returned back to his self well..almost..now when he was seeing Haru , he was blushing, a lot. Sometimes he couldn't speak well, and was messing up his words and ideas to point that he couldn't get near Haru without getting ridiculous in the process. On top of it, his voice was acting weird. Sometimes it would go loud, sometimes quiet, sometimes high-pitched, sometimes very-low pitched, sometimes sounding really weird.
For a moment, because of it he wasn't speaking at all and man, how much it scared Gokudera, Yamamoto too (yes even him). Before that could get on one of the roof if Namimori High School a.k.a the QG n°3 (the first being the Vongola mansion and the second being the Vongola base which is currently getting built. Tsuna did became Vongola X at almost 16 years old after some important event which would be explained later), Gokudera and Yamamoto dragued Tsuna somewhere else, that Gokudera bowed, pleading his boss to speak and tell him if he was angry at him for not being an enough good right hand man. Yamamoto spoke too asking him if something was bad happened to him, and telling that as his best friends he could speak about it to them. Tsuna sighed, being flustered of this embarrassing situation, he spoke with his total weird voice,which surprised the two guardians and said to Gokudera and Yamamoto that if he wasn't speaking all this time it was because of his voice was acting weird lately. He then added that nothing bad had happened nor that he was angry and that Gokudera was an excellent right hand man. Gokudera was really proud here.
Haru who was worried that the 3 boys didn't came to eat until now, came near them. She saw that Tsuna was blushing a lot and seemed bothered, even if it was his best friends he was talking to, he couldn't stop himself from being shameful that they were hearing a such voice. Haru came and hugged Tsuna, asking if something was wrong, of course Gokudera yelled at her, claming that the Tenth wasn't feeling good and that she was making things worse. She yelled at him back claming that she had all tight to be worried about Tsuna and that was trying to comfort him. And so on a raging battle between the two began. Even with Yamamoto trying to calm them, they didn't stop until Tsuna spoke saying that he didn't want to see his friends arguing. Unfortunately for the recent mafiosi boss, while he was shouting do they could hear him, his voice went lound, quiet, high and low, all in the same sentence. Haru looked at him confused. He face went all red like a tomato no like a red piment. He hide what he could hide if his face along his long front bangs and ran at such speed that it was almost as if he was chased by thugs, very dangerous thugs.