Hey so yeah, it's a filler because there was an idea in my head and I really needed to write it down. So here it is. Not a long filler but it does include some explanation which will be mentioned in the later story and I thought this is the best way to introduce it to you other than me just rambling about it in the author notes or just writing it in the additional lexikon.
But I hope you enjoy it and I'll give you a bit more of an explanation at the end.

~Filler 3 - Relaxing~

Izo was irritated. That was something he hated. It was annoying. Why couldn't Thatch let it be? The black-haired division commander sighed. He couldn't get any rest at the moment. So Izo did the only thing he could.

The marksman took a bag and left his room. There was only one place other than his room where he could truly calm down.

Luckily, he didn't need to walk far. His destination was in the same corridor as his own room. Izo knocked on a door and opened it without waiting long.

"You looked annoyed, yoi", Marco remarked when the younger commander turned to him. "Not annoyed. More irritated", Izo mumbled, dropped his bag, and let himself fall on the blonde's bed. He could hear steps and then felt that Marco sat down next to him. "Want to talk about it, yoi?"

Izo turned his head to look at the younger one. It seemed like he didn't need to say anything because Marco laughed and stood up to lock the door before coming back to the bed.

It didn't take long before Izo was comfortable resting his head on the blonde's chest while the younger man carefully stroked his head.

"Thatch is irritating me… I told him that I am not interested in him the same way as he is in me. But I still get favors from him", the crossdresser said softly. "Maybe he just wants to spend your heat with you. After all, you are the only omega on board who doesn't choose a heat partner and you are always very weak after your heat, yoi."

Izo sighed. "If it was just that, then he could tell me directly. But I also don't think it would be better if I choose a heat partner. Because it only really calms an omega when they are attracted to the alpha and I can tell you personally I am attracted to no one on board."

That made Marco stop in his stroking action. "But didn't you say last week that Vista is attractive, yoi?" "I said I can see why people say or think that Vista is attractive. But that doesn't mean that I am personally attracted to Vista. It's a difference. To be honest with everything I know I think I might be scent-sexual."

"Scent-sexual?"

Izo lifted his head to look at the younger one. "I thought they would have taught you… Well, looks like now is a good time. You know how people are basically divided into two birth genders and will also be divided into three others when they reach a certain age, right?" Marco nodded. "So when an omega is attracted to betas in general despite the birth gender, the omega is beta sexual or short b-sexual. It is the same with other genders. There are alpha sexual, beta sexual, omega sexual or the short terms for combination ab-sexual, bo-sexual or ao-sexual."

Izo paused to see if Marco had a question on that part. But since there wasn't the omega continued. "These sexualities are expanded by the birth gender. Some people are only attracted to women disregarding their second gender. These people would be called female sexual or simply f-sexual. People who are only attracted to males are male sexual. There can also be combinations with the second gender but that will be a bit complicated to name all. But if you are attracted disregarding first and second gender you would be called tutti sexual."

"Okay, but you said scent-sexual. Is that a special case, yoi?"

"Yeah, it is. It does sound rare but it really isn't. Scent-sexual means that you are only attracted to your scent mate or soul mate. So yeah… I don't find any person on the ship attractive and we have over a thousand members. So the chances are quite high."

Izo felt how Marco's hand started to move again and that the younger one returned to stroking his black hair. The marksman laid his head down again and closed his eyes.

"So even if you would take a heat partner there is a chance that it wouldn't really help you, yoi?" Izo just nodded. It was more relaxing for him now just to lay here with Marco.

Even if he wasn't attracted to the blonde, he found a certain comfort in the scent of the younger one. It gave him a certain peace. Also, Marco was easy to be around.

He liked the blonde. He liked him like a brother. Even when they first met many years ago before Marco was reborn he thought the same. The only difference was that back then he viewed the blonde as a slightly older brother and now as a younger brother.

"But… if you want to help… after my next heat, could you get me some food and stay with me for the post-heat?", Izo asked quietly. Because Marco was nearly the only person except for Tess and some of the nurses who he would be okay with when they entered his room.

"If it helps you, sure, yoi", Marco said and Izo could hear the smile on the face of the blonde.

So yeah, since we have so many sexualities in real life and I didn't feel like it would be right to use any form of known sexuality for this story as yes, it might work with hetero- and homosexual at the basic for just the birth genders. But with the a/b/o system, it just felt wrong. Even if I would have include transsexual or other sexualities. I felt it would become too complicated and there was also the risk of writing it wrong. That is something I dislike to do even if I can research it, with how many gender and sexualities there are, it would be a pain in the ass to integrate everything accordingly without being disrespectful to anyone who identifies with a certain gender or certain sexuality.
So my conclusion and easy way out was that in this story a person's sexuality is either based on their second gender or their birth gender depending on which gender they prefer.
For example, Sanji would be female sexual, as he prefers this birth gender and doesn't care about the second gender of a woman.
There are the possibilities of combinations like abf-sexual, which would mean that the person is attracted to either female alpha or female betas. So I think with the combination it will work for this fanfic.
I hope everyone can understand why I choose it that way.

And stay healthy everyone =)