There was a lot between Tsuna and Mukuro, with Mukuro *ahem* wanting Tsuna's body, and grabbing Tsuna from behind while whispering into his ear and resting his chin on his shoulder. Tsuna seems dead set in thinking that Mukuro isn't so bad despite everyone telling him otherwise, and is revealed by Reborn to have constantly, since their fight, been asking about Mukuro's well-being. Although their relationship became arguably less antagonistic ever since Tsuna beat him and Mukuro became his guardian.
During their fight if you replay the part where Mukuro grabs Tsuna from behind, headbutts him, and pulls him back up by his arms to rest his chin on his shoulder and whisper in his ear it sorta looks like they're having sex.
In Chapters 366 and 367, Mukuro and Tsuna have their second battle and Mukuro seems genuinely happy to see and fight Tsuna again.
In Chapter 380 and some chapters afterwards, Mukuro and Tsuna fight together.
In Chapter 383, Tsuna grabs Mukuro by the shirt and pulls him close telling him that he needs to help Chrome as she's his comrade. Mukuro doesn't respond and Tsuna gets upset saying that he didn't think Mukuro would act this way, indicating that he had respect for him and expected better of him. Chrome also reveals her obvious feelings for Mukuro and says that she likes what he likes (we then get a picture of Tsuna and his friends and Mukuro's comrades.)
Mukuro has a bit of In Love with Your Carnage towards Tsuna. For example, in chapter 385 he's shown looking quite pleased when he sees Tsuna defeat a foe and remarks that "He's gotten even stronger."
It's unbelievable how fast Spanner x Tsuna spread within the small amount of time they were shown together, and the mangaka seemed to be feeding the fans by having Spanner strip Tsuna naked and handcuff him in a bed. Plus the way Spanner blushed and got the trembles when Tsuna mentioned his X-Burner...
Hibari's obsession with beating Mukuro seems to be the closest Mr. Axe Crazy will get to showing actual interest in people...
Hibari is actually quite pacified when Reborn mentions to Hibari as he is about to go on a rampage that he might be able to challenge him in the future if he was patient. And when Mukuro got out of prison? Went to meet Hibari. Well, sort of.
The Hibari ten years into the future seems to have developed quite an interest in Tsuna as well... seeing how he really enjoyed their fight and even told him that he's starting to *cough* excite him the same way his future self did.
Byakuran and Mukuro! There is an unbelievable amount of stuff going for these two. I mean, what with Byakuran acting very friendly and discussing the meaning of flowers with Mukuro.
Byakuran and Irie. Even after it's revealed that Irie is actually working against him, Byakuran doesn't behave any differently with him. Then again, he'd figured it out a long time ago.
And to Tsuna. While Byakuran is trying to kill Tsuna and his friends all so he can take their Vongola Rings he seems to enjoy taunting Tsuna's abilities and playing with his emotions a little too much. In addition, after Tsuna absorbs Ghost he shows up and compliments Tsuna in his own weird way saying Tsuna is a "very curious person" for being able to get Xanxus and Mukuro over to his side even though they too once tried to kill him. Tsuna remains determined to defeat him even though Byakuran clearly has more power. This impresses Byakuran to the point where he admits "I admire your spirit, Tsunayoshi-kun. I've been waiting for this fight for a long time." All throughout the battle we see Byakuran ruthlessly attack Tsuna and taunt him with things like "Very scary, aint it?" while clearly enjoying the nervous/shocked expressions on Tsuna's face. Also, from the ending of Chapter 275 all throughout Chapter 276 we see Byakuran stealing a page out of Mukuro's book by grabbing Tsuna from behind and suffocating him—meaning Tsuna's all flushed, gasping, weakly fighting back, etc. while Byakuran never stops smiling, calling him Tsunayoshi-kun, and breathing things like "look at how helpless you are..." into his ear. Tsuna desperately tries to free himself from Byakuran's hold but is unable to and Byakura reacts to this with disappointment saying "I was hoping for a better match..."
Yamamoto and Squalo. But that's a case of Yamamoto being a very Friendly Enemy to Squalo, despite the fact that Squalo hates him.
Glo Xinia had quite a bit of this going on with Chrome. Considering how during his fight with Chrome he grabbed her hard enough to cause her pain, kept getting in her face, and told her things like: "You seem to like being touched by men. Your blushing cannot betray your desires." "Give me MORE!" (after hearing her screams of pain) and "It's time to eat... that ring and you!" It's hinted he might've done something to her had Mukuro not shown up, allowing her time to escape. Also, when fighting Mukuro he comes out with this line: "Is that girl so precious to you? Then I'm going to take my share of such a precious girl right before your eyes. This could just be the best situation, don't you think? My appetite for that girl just keeps getting better!" and "Don't worry Chrome, I will take good care of you for MUKURO TO SEE!"
She was once tied up, with a smiling Bel being very close to her with a knife.
Depraved Homosexual Lussuria towards Ryohei. It starts getting ever so slightly disturbing when he's hitting on jail bait, and is insinuated to have necrophiliac tendencies as well. In his words his favorite bodies are the "wasted, cold, unmoving" ones. Unfortunately, Ryohei goes topless during his fight against Lussuria and this only serves to make Lussuria his hardcore fanboy. In fact, Lussuria actually openly ogles Ryohei's muscular physique and refers to his body as "pretty nice", says that he's "just his type" and promptly decides to take him home and make him a part of his "collection" after he beats him up.
And Julie Katou /Chrome as he expresses interest in Chrome and kidnaps her, telling her they have "date plans" and lets her sleep in his bed (although he is actually the first Mist Guardian, Daemon Spade, so it isn't a Katou/Chrome, but a Spade/Chrome instead) . He also finds her to be "so damn cute" and in Chapter 309 Chrome awakens in his bed, he enters the room, offers her a change of clothes, gets onto the bed with her, grabs her face, gets real close and asks if she needs help changing. He then says they should "get to know each other, real nice". Yep.
And let's not even touch all the implications of his desire to possess Mukuro's body...
And now we have Enma/Tsuna and Aoba/Ryohei.
During their fight Shitt P. invades Gokudera's personal space (i.e. wraps her arms and legs around him), calls him cute, and says that she loves him.
Bermuda/Reborn. In Chapters 385, 386, and 387 he asks Reborn to join him and says he likes him and wants him (for his team). He kidnaps him when he refuses.
Lambo/Reborn. Lambo seems to have a bit of a Tsundere relationship with him and treats him as a rival although Reborn just sees him as an idiot. And although Reborn beats him up at every chance, he does still seem to worry over him.