Much like Log Horizon, I did a whirlwind marathon of Gundam Build Fighters last year as the first season was finishing up and absolutely fell in love with it and was completely on board for the second season. It is seven years later and features a mostly new cast but I'm going to say that yes, you should see the first season first. It'll help you in the long run and come on, if you like this you'll want more of it and that's 25 episodes of more right there.
Gundam Build Fighters Try
Seven years after Sei and Reji went far in the Gunpla World Championship, gunpla has changed a little bit and now teams of three are the norm for battles and the game is more popular than ever. Fumino is trying to keep her school's team going, centered around the club that Sei formed, but she's not having much luck when she drags in transfer student Sekai whose never even heard of the game before but whose martial art skills make him a surprisingly good fighter. Add in China's younger brother Yuuma, who's a double threat with great building and fighting skills, and the local championship might actually be within their grasp!
To summarize this review in a sentence, this season was 90% as good as the first season. The visuals and music remained largely unchanged and as solid as before (I didn't even know the soundtrack had such fun titles as "Is it Wednesday Yet?" or "Yes it's only two cour") but the story suffered a little bit. Let's start with the positives however: the first season had very few female characters (both as mains and one-off side characters) and this season brings in more on both counts. It's still far from a 50-50 gender split with teams typically only having one female member and there are only one or two all girl teams but we see more of them at every level and the story even starts out focusing on Fumino. Sekai eventually steals the spotlight from her in typical "shonen ace" fashion (and the show never takes him to task on his hotheadedness and initial lack of teamwork like it should have) but Fumino, and the other girls, has motivations that are the exact same as the boys and no one ever questions her for being a player or for being the leader of Team Try Fighters which in and of itself is a hugely positive thing (heck her personal arc is about not limiting yourself to being just a support which is amazing considering that's what girls usually are reduced to in these fights, even her big opposite is ultimately a fighter and her team's healer). There is a beach episode involving models and a gunpla race but it didn't feel like unnecessary cheesecake or fanservice, it was presented more as a "wow gunpla really is in EVERY part of life!" moment and it was funny to boot. I thought that the series wouldn't flesh out Sekai's model sister Mirai that much and while she's still very much a minor character she was a lot like Sei's mom from the first season, often present and important in her own role.
One step down from the first season however was how they handled the side characters, in the first season reoccurring characters (like Mao and Tatsuya) were introduced early on and then came back for multiple fights all the way up to the finale. It was very satisfying seeing everyone get better and made the show feel less like it was just a tournament-style fighting shonen (which it is to an extent). This was partially made possible because Sei and Reji could and would lose, the fights had higher stakes and since it wasn't until halfway through the series that the fights became knockouts it kept those side characters around. Here the fighting is set up much more conventionally and if Fumino/Sekai/Yuuma lose one match they're completely out of the tournament so of course they can't lose and so the most intense matches are the ones without them in it. I've defended some series before which have had the "the characters can't lose or the show ends" idea in them (like the similar to each other Captain Earth and Star Driver) but since the first season did manage to avert this idea it just feels like lazy writing here, maybe the six month turnaround between seasons was too much for the staff to give it their creative all.
So not only did the fights lose some of their drama but it also means that characters from the first half of the show have very small roles in the second half which was unsatisfying and strange since some of them like Gynako and Shimon still pop up every few episodes or so. I do have a theory about this which wouldn't make the show better but would explain it; I think that we're getting another sequel, a direct sequel this time, set at the world championship and that these side characters will be reappearing in those qualifiers or in the final tournament themselves. The fact that several prominent characters from the first season never made even an on-screen cameo suggests that (geeze Sei, I know being oddly mysterious about gunpla kinda runs in your family but not even having your name mentioned in conversation until around the 20th episode is ridiculous) and it just felt like there were a few ideas brought up early on that were quietly put to the side. Honestly I'd love another season because this show still is so much fun even with those problems. It never failed to make me smile, I'm picking up more references than before, and I'm glad that both the characters and the staff seem to agree with me that the best gunpla fight is the silliest battle royal that it can muster.
And something that makes me smile even more, it's (sort of) licensed now! Sunrise and The Right Stuf/Nozmi Entertainment have reached and agreement where TRSI will be handling all of the gundam releases in the US now and they intend to put out a fair amount of stuff. There's no date for GBF yet but they have said that they are aware of it's passionate fanbase so fingers crossed for news before the end of the year! In the meantime, like it's predecessor GBFT can be found streaming on the Gundam Info youtube channel for free with English subtitles, it's interesting to actually see the streaming numbers for once and makes me wonder if it's 10k+ views are high or actually average for streaming anime the week it comes out.