@K00K13: yep, I'm the type who thinks 'ship and let ship', that people should ship whatever they want and let others do them same, so I'm not going around insulting people if they want to root for Rei with Arsenio, it's just not for me. I haven't ship them at all at any moment, and thought many times that Rei had a better relationship with Llod (who's 17), especially at the beginning - except that clearly Llod is in love with Eric and it seems very much reciprocated, just Eric seems to have been thinking until now that Lloyd should be with Rei. Anyway, I wouldn't have minded if that ship have become end game as long as they got together some time in the future, but here with really have Arsenio lesting after a 15 year old because they have those big boobs, and even though he was guilty about that it still doesn't change that the teenager who has a huge crush on him is quite pushy and Arsenio just goes with it, and yeah I'm not a fan of that. Rei really is very immature, it's not just a question of an arbitrary number, they still have A LOT of growing to do.
I don't think that Arsenio is in love with Rei too btw, like I think (in addition to be sexually attracted to them) that he cares about them yes, but I think that after that time Rei confessed to him the first time, he just confused his lust + the super gratefulness he felt at someone loving him, a monster, with love.
As for shipping Sauro and Arsenio, I'd say it's safe to think it's a possibility, I think it's either the end game or Arsenio still is undecided by the end of the story, especially because he might also be undecided what form he's most confortable in. But their chemistry really is super high level, it only took a few chapters to make obvious how much they care about each other, adding to that the way Arsenio looked every time he mentionned Seuro in previous chapters, and those covers, and the prequel... there is just too much of a "(childhood) friends to ennemies to lovers ultra combo" vibe to them for this ship not to be serious. So yeah imo nobody should feel weird about shipping them
Plus like I was saying earlier, the possiblity of Arsenio forging Excalibur for Sauro, and the kind of magic they use, makes it just too good to not see an awesome battle couple right there, while Rei's magic is quite not compatible with Arsenio's body. So well we'll see
ps: as for being bothered by being called a fujoshi... have you ever tried reading/watching stories with f/f pairings? Like, there are some good yuri here, or the anime Mouretsu Pirates, or if you watch cartoons rooting for pairing in Steven Universe etc? Or stuff with trans characters, like that cute little manga by a trans woman, Hanayome wa Motodanshi. Though you shouldn't mind what other people's think about you imo, but if you still can't help feeling guilty, less chances you're a fujoshi if you like all kind of pairings ¯\_(ツ)_/¯