The simple fact that despite all the trauma and hardships that the three of them had faced ever since first coming to Melromarc; they're reactions at opening trust with one-another and using the different strengthening methods makes it seem like they are kids opening Christmas presents.
Just the entirety of Chapter 61, during Melromarc's celebration of the heroes stopping the next Wave of Catastrophe and the war between Melromarc and Siltvelt, where the heroes and their party members start to further their bonds. Specifically:
Motoyasu of all people actually helps to lift Naofumi's spirits when he is haunted by the memories of the people he failed to save. Naofumi is understandably, but pleasantly, surprised by Motoyasu's counseling skills, comparing him to a big brother figure and starting to bond with him. Motoyasu even goes out of his way to arrange a dance between Naofumi and Raphtalia!
Naofumi and Raphtalia's dance, discussion, and kiss in a peaceful environment, which also allows Naofumi to come up with a plan that will satisfy both him and Raphtalia.
Itsuki not only helps Motoyasu's plan for Naofumi and Raphtalia by playing on the violin, but he also further bonds with his party by reinforcing his promise to Crystal to help her find her friend. Itsuki and Rishia also have a heart-to-heart conversation, with both of them giving each other a You Are Better Than You Think You Are speech.
After Melty tearfully admits to Filo how much she misses the father she loves after seeing how broken he is, Filo shares her experiences with Naofumi and encourages Melty to tell her father about how much she feels. This actually does help Melty get through to her father, as they and Mirellia share a moment together, hugging, crying, and wishing to be the happy family they once were again.
Ren and Wyndia have a heart-to-heart moment where the latter tearfully tells the former just how much she cares for him as her friend and teammate, with Ren admitting how much he cares for his teammates and promises to never push them away again. Even though Wyndia doesn't get to admit how much she loves him, she's satisfied with Ren's words for the time being and decides to wait a little longer.
During the fight with a Cursed Series Itsuki, Rishia remembers her promise and gets through his crazy state by hugging him.
Motoyasu helps the children that were captured understand what Itsuki was going through to fall into the Cursed Series. The children decide to help Itsuki as best as they can so he never falls again.
At Cal Mira, Rishia goes out on her own but gets into trouble when attacked by several monsters, with Itsuki rescuing her just on time. Rishia begins to cry because she feels weak - but Itsuki tells her that she's a fundamental part of the team, no matter what she feels like, and gives her an Affectionate Gesture to the Head. The way he does it, it's almost as close as a declaration of love as he could without actually saying the word.
Therese helps Wyndia get through the mental blocks that kept her from using her Dragon magic to the fullest - by helping her get past the trauma of losing her father and getting her to truly admit (to herself) her true feelings for Ren.
At the beach, Naofumi and Raphtalia enjoy the moment of relax by cuddling together.
After L'Arc and Therese reveal that they had planned to kill the Cardinal Heroes to save their own world, but don't seem keen on attacking first, Naofumi, inspired by his own willingness to forgive Ren and Itsuki, drops his shield and challenges L'Arc to kill him, banking everything on their friendship. L'Arc seems to be ready to do the killing - but instead stabs the whale, crying out that he can't. The two groups stand down, because none of them want to hurt the other.
When Glass comes, L'Arc and Therese attempt to convince her to stand down. It doesn't work, but kudos to them.
Even after Glass threatens to kill them all, when she is at their mercy Ren doesn't kill her, instead choosing to let her and the others go, in payment for her sparing their lives during the Third Wave.
When she later begins to slip into her version of the Cursed Series, the duo manage to convince her to stop, holding onto her even as she burns with the fires of her Cursed Series, reminding her of a friend of theirs and her likely reaction if she falls too far or dies.
When the three heroes from other world leave, the Heroes and their companions feel despondent because they really liked them - but they bounce back with a promise to find a way to save all the worlds that are being threatened.
The best thing is how they come to that decision. Ren seems ready to ask the others to do it even if it sounds crazy, but Itsuki agrees to help before Ren even finishes the question, and Naofumi quickly agrees as well.
Ren pleads with Wyndia for her help in finding a way to save L'Arc's world, and she gives in and agrees, saying she doesn't want her friends to die either. Ren then embraces her in a big, thankful hug, almost putting the dog girl through a mental meltdown.
Ren and Wyndia end up going on a sort of date, where neither is sure if it is a date or not since Wyndia is teaching Ren how to swim. However, due to various reasons, by the end of it, the two are closer than ever.
After Naofumi has his final Heel Realization over how badly he hurt the people he loves, Queen Mirellia - even when she's clearly furious over Naofumi's hurtful words towards Melty - is willing to tell him just what he needs to hear so he knows what to do to fix his relationships with everyone.
As the fight to save Melromarc from the Spirit Tortoise approaches, the Heroes and their people do their best to say the things they wished they could have said sooner.
Naofumi apologizes to Ren and Itsuki for his actions during his jerkass phase. The other two forgive him and state that they too need to apologize.
Wyndia and Rishia spend time together, with Rishia explaining to Wyndia why they should accept that Ren and Itsuki are forgiving Naofumi in spite of what he did.
Ren and Wyndia finally have their mutual Love Confession and Sacred First Kiss. Wyndia tells Ren that they'll continue their 'talk' after they beat the Tortoise.
Rachel spends the night with her husband.
Aksel and Maya sleep while holding hands.
A small yet beautiful moment, when Filo makes it to her parents right before the battle with the Spirit Tortoise, and the family reunites for a moment of happiness.
Then Naofumi takes advantage of Filo's connection to Fitoria to talk to the Filolial Queen... and thanks her for taking Filo away, apologizing for his actions and for betraying her trust, and telling her that he and the other Heroes are fighting to save the people. This moves Fitoria so much - reminding her of the Heroes that sealed the Spirit Tortoise so long ago, when she still had faith in humanity - that she decides she can be Neutral No Longer and teleports so she can join the fight and save these Heroes.
After the battle, Naofumi begins to look for Motoyasu and Ren, who have disappeared (kidnapped by the Hero of the Book). While seeking them, he learns that the last thing Motoyasu was seen doing was running along with his party to fight off the Turtle for long enough to let an entire city evacuate. They were successful. Naofumi even mentally salutes Motoyasu, lamenting his previous misjudgment of the man.
When they find and rescue Motoyasu's party, they gain the hope that they can also rescue the heroes.
The girls forcing Wyndia to stay put and realize that she is not alone and that they're going to help her find Ren, no matter how much she tries to push them away.
Ost, in general. Even though she is the soul of the Spirit Tortoise, the Heroes can't help but like her for her sincerity and willingness to help. And the knowledge that killing the Tortoise will also kill her only makes them try to find an alternative.
The Four Heroes having a Group Hug after the fight with Kyo. Considering how bad their relationship is in canon, seeing them be like actual brothers is wonderful.
Naofumi, Raphtalia and Filo hugging Ost as she begins to die.
Wyndia thanking Therese for everything she's done to help her out.
The story of Keichi and Nausicaa. Keichi was the Hero of the Sword and behaved similarly to Motoyasu - but that changed when he met Nausicaa, a dog girl from a village Keichi had just saved from a Wave. The two fell in love, fought together in the next Waves, married, and had a son - but then, during the fight to seal the Spirit Tortoise, Nausicaa died and her soul was absorbed by the Tortoise. However, Nausicaa's love for Keichi was so intense that she was able to affect Ost, prompting her to do good for the people of the world and teaching her compassion, while Keichi remained always faithful to Nausicaa and taught their son and everyone else that wanted it the sword fighting arts the two of them had developed. When Keichi was on his deathbed, Nausicaa managed to take control of Ost just long enough to be able to speak with Keichi... and when he died, instead of absorbing his soul, Ost released Nausicaa's so the two could be Together in Death. Making the first conscious decision on her part that changed her life forever.
Ost doesn't die: instead, she lives on inside of Naofumi's Shield, forever able to accompany the man that did so much for her.
Wyndia pouring out all her feelings for Ren into a heartfelt Love Confession, and Ren finding closure from Bakta's and Welt's deaths as he promises to make Wyndia happy. Because of her, he unlocks the Sword of Bravery.
After multiple harrowing events, a sprout of hope shows when Naofumi, Rishia, and Kizuna finally encounter Itsuki, and Rishia glomps him in utter joy.
Kizuna remembers how the King of Sickle (L'Arc's father) took the time to become her Parental Substitute due to how she was summoned at just age twelve. Judging by what she says, he did a great job at helping her get used to the new world.
Naofumi rescuing Filo.
After everything they have gone through since they arrived to Glass' World, Naofumi and Raphtalia finally find each other.
A figure stood in front of him, surrounded by the mist she'd created. She was dressed in a white and red Miko outfit. Her hands gripped a katana with a green gemstone in its pommel. The gemstone was the same color as Naofumi's eyes. But what drew Naofumi's attention was the back of her head. Her hood was down, revealing very familiar hair braids and animal ears. The mist gave her a true Otherworldly aura. Like a figure from a fairy tale coming to life before his eyes. "Don't worry, Naofumi," Raphtalia spoke, still facing Trash and his compatriots. "Your loyal sword... has returned!" "Ra... Raphtalia?" Naofumi choked out. Naofumi's hands gripped his shield tightly. He looked down at the ground in front of him as a sob racked his chest. "Y-You couldn't have gotten here sooner?!" Even though he said that. He was smiling wider than he ever had before. Tears of relief fell down the sides of his face as a block of ice in his chest slowly melted. Raphtalia smiled in return. Everything was right in the world now. Whatever happened next, the two of them were going to be ok. Because they'd found each other again.
Glass is beyond happy to finally be reunited with Kizuna.
After being reunited, Naofumi and Raphtalia end up flirting with each other and really need to get a room to themselves as they find how the other looks now in the new outfits and the like EXTREMELY hot.
Glass hugs L'Arc from behind in a true display of friendship after all the times he's helped her when he feels Rage over learning Trash had murdered his former childhood friend, the former Katana Hero Kenshiro. And she then asks him not to give in to that feeling like she had so long ago when she despaired. It works, to a degree.
Naofumi and Raphtalia finally having Their First Time, and declaring their love for each other. They even begin to think about having a bigger family.
Itsuki and Rishia using their ofudas to text to each other like two smitten teenagers unable to express their feelings for each other out loud. Rishia ends up hugging her ofuda as she realizes that Itsuki does actually like her, even if he can't say it yet.
Kenshiro manifests to L'Arc so they can finally find closure from the former's death. Even Kenshiro Trolling L'Arc by stalling him so he'll get caught by Therese is this, because L'Arc knows it was something Kenshiro would have actually done if he were alive.
Kizuna and Glass beginning to repair their broken selves. The two of them are still fighting the depression from Kizuna's imprisonment in the Labyrinth and their separation, but together they might be able to restore every broken piece to its rightful place.
Ren is shown slowly recovering from the dual shock of undergoing his Curse Series and the torture within the Spirit Tortoise. With everyone's help, particularly Wyndia's, the young, broken teenager begins to find his way back to the light.
When Melty confides in Eclair how she's having a hard time thinking of forgiving Naofumi for what he did, the knight tells her that she knows it is not an easy process, but that eventually she might be able to do so.
Eclair comes into Dou-Lon's room and makes sure to organize it, admitting that she misses the hakuko. Whether Ship Tease or Vitriolic Best Buds, it's obvious that she considers Dou-Lon an important part of her life.
Rino decides to leave Lurolona so she can help hunt down and kill Malty for everything the bitch did to her. Motoyasu, after begging her to stay without success, hugs her and begs her to return, telling her she'll always be welcome in his house.
When Ethnobalt feels he has not contributed enough to fighting a Wave because he's weak, Itsuki gives him an intense You Are Better Than You Think You Are speech, encouraging him to keep working with the others and find new ways to support.
As he does, he also gives a flaming praise of Rishia, her skills and her determination. This kid's clearly head over heels for Rishia.
Raphtalia notices that the food she's got is exactly the same Naofumi made after the fight with the Orthrus Dog. When she attempts to thank Naofumi, he replies that the one who made it was actually Filo - who exclaims she did it because she wanted to do something for her parents. Raphtalia hugs Filo with Tears of Joy.
Aksel telling Dou-Lon about how much he loves Maya and wants to be next to her.
This chat also begins to prompt Dou-Lon into realizing he may have feelings for Eclair.
Aksel and Dou-Lon reminiscing about the friends they have lost.
Hoshi, the Ofuda Hero, finally begins to come out of his shell, thanks to Filo and Raph-chan.
Hoshi later meets with Naofumi, and the two bond over their past and how they were summoned to their respective worlds.
Rishia finds Itsuki depressed because he had resorted to the Cursed Series. She hugs him, holds him while he rambles, and tells him she'll always try to help him. Itsuki gives her the green gem flower he found in Lazuli, and is briefly reminded of the friend he lost in his original world before swearing that he'll do everything to avoid losing Rishia and settling to sleep next to her.
Naofumi outright thinks of Itsuki as his younger brother, and gives him a grip for his Bow's string - because he still remembers how Itsuki's fingers bled during the first fight against the Spirit Tortoise. Itsuki hugs Naofumi in thanks.
Kizuna cheering up Akane after the latter mentions her (quite sucky) pre-isekai life, telling her that, even if she did a rather lackluster job as a Hero, her work as a clothesmaker helped people be a bit happier.