Three hundred years. It is easy to say those words and equally be unable to grasp such time passing. However, one of the True Dragons knows what it is like in isolation, cut off from the world in a cave, unable to do anything but wait that time out. Veldora. That is why when the first person he met threw themself at the barrier sealing him in place, he was excited, even if it was a slime. Following in after the slime, as it moved around aimlessly, was another that stepped in and picked it up.
The other creature was bipedal, definitely not a human despite his form, and something about it nagged at him. He knew what it was but didn't want to say anything at first. Why would he start hounding the thing with questions after just meeting? These were the first guests he had in ages! So it was best to make the first move and greet them to show he wasn't hostile. Veldora had and they were found to be interesting.
Eventually, what the other creature was, F/N Tempest, was brought up. Dragonoid, the offspring of a True Dragon and a human. Not exactly a common sight, for one to appear in Veldora's cave and for him to be an Otherworlder was more unlikely. At that time, he had accepted it as chance, a thing that could happen despite knowing that, his niece, is the only Dragonoid in existence. Or was supposed to be. He accepted it all the same.
After Rimuru used [Predator] on the seal with Veldora in it, he watched through the slime as the two explored the cave and spoke about the world. He was mildly envious of how they were having fun. Once the seal is gone I'm making up for the lost time with them! He declared to him, alone again. A few more years working on breaking the seal was nothing compared to the three hundred he had spent in the cave. As so, he found some texts to keep him entertained. And now he could see the world in a way, it was an overall improvement.
What he didn't enjoy hearing was this corruption he heard Rimuru and F/N talk about. What was it? Veldora didn't know! Something this unknown was rare for an immortal being like the Storm Dragon. It warranted investigating! If he could... He couldn't. In fact, inside Rimuru's stomach, no one could hear him, meaning it wasn't as if Veldora could request F/N to visit so they could talk about it.
Then Rimuru and F/N split up for a time. Fool! Veldora shouted at Rimuru. Don't leave him alone to watch over the goblins, take him with you so he's safe! Not that the almighty Storm Dragon, one of four beings, godlike in nature, was worried about F/N or anything. It was just that Dragonoids like him need someone powerful watching them, or they might do something bad. Veldora would know from personal experience, having destroyed a town himself, and his niece having destroyed an entire nation!
Thankfully nothing bad happened... Until F/N threw Rimuru so hard at the ground in a drunken rage that he was worried the slime would die. Who knows what would have happened to Veldora if Rimuru perished while he was in his stomach! Thankfully, again, nothing bad happened. Though F/N's departure from the village to stay with the ogres bothered him.
Now enter Ifrit, the fiery spirit that once dwelled inside Shizu and was now calling Rimuru's stomach home. When he first arrived, he was attempting to break free when Veldora spoke up, telling him it was no place he could break free from, that Rimuru was not someone he could take on. The spirit recognized the Storm Dragon, sending into him a shock that completely removed his desire to fight. That tends to happen when one faces a being at the top of existence.
"I would have liked to see those two fight you together," Veldora said to Ifrit, "But perhaps there is a better foe out there for them. Perhaps I should challenge them!"
His laugh tossed Ifrit off mentally, however, he quickly accepted and respected the being in front of him. So the two watched together as things unfolded, including when F/N hugged Rimuru. Veldora is mature enough to not tease them during a difficult time for both of them, after all. However, unlike Rimuru, Veldora could tell F/N was thinking about killing him. How exactly? The eyes of a Dragonoid pierce through many things when they lock on a person they have killing intent toward. He didn't kill Rimuru though, that was good, for both Rimuru and Veldora.
F/N was going through a troublesome time, so troubled that he asked Rimuru to eat him. With [Predator] you perverts! Veldora, as if by nature, already knew what he was coming for. He found that strange in an interesting way. And so when F/N asked Veldora to be his father, he was more surprised at how F/N asked than the fact that he had asked. Just to make sure it wasn't a joke, he attempted to laugh it off.
"You certainly had me there for a moment, I know Rimuru joked about it but I didn't expect it from you!"
"That wasn't a joke."
Those words caused him to freeze, was his feeling really right? Well, a moment later and he was F/N's father. Veldora took a moment to think about what had happened while Ifrit and F/N fought, causing him to only cheer instead of teaching him anything. Why did he so easily agree to it? Sure, he could be described as easy-going and impulsive, but did he desire to be a father? Certainly not. The thought never crossed his mind. So for the thought to enter his mind and be agreeable in an instant was odd.
"It seems our time is nearly up," Veldora spoke up.
"Really?" F/N asked, letting go of Ifrit's neck.
"One gets a rather good sense of time when counting is all one can do in a cave," Veldora chuckled to himself. "Be sure to take care of yourself out there."
"I will," F/N said, "And thank you both, I mean it."
"Until we meet again," Ifrit lowered his head, holding no grudge to the losses he endured.
Once F/N was gone, Veldora spoke up again, "Hmm, I'm worried for his future."
"I am not sure, but I believe that is a part of being a parent," Ifrit replied, turning to the True Dragon.
"No, this corruption, I fear something greater is at play here," Veldora looked up to watch what was going on outside, "I do not know if it cares whether he lives or dies, but if I can, I will make sure he lives."
"If there is anything I can do, I will do what I can," Ifrit lowered his head to him.
"That's just it, I am unsure if either you, or I, could stop it," Veldora looked at Ifrit, "But I am pleased to hear that all the same."
"Wait, something you cannot stop?" Ifrit asked, rightfully so.
There were only a few that could stop a True Dragon and Ifrit did not have the strength for the challenge. Neither did F/N from what he saw. The fights were one-sided, there is no denying that, but there was a big gap between F/N and a True Dragon. One reacted to the world-changing, the other had the power to change it. What was the most troubling, that told Veldora enough, was how F/N did not get nearly as much power as Veldora was expecting. It was so little that it made him pray a little inside. Of all the True Dragons, the last one anyone would think would pray was him, Veldora.