26 Episode fantasy/comedy Anime from 1996, season 2 of 5 of an anime based on Hajime Kanzaka's light novel series from 1989 and the last one that followed plotlines as described in the books.
The song is "Give a Reason" by Megumi Hayashibara, who also voices the main character Lina Inverse. Megumi Hayashibara is a very prolific voice actress and musician, who has appeared among other thing, in Maison Ikkoku, Bubblegum Crisis, 0080 Gundam, Ranma ½, Patlabor, Neon Genesis Evangelion, Pokemon, Cowboy Bebop, etc.
Slayers is a really good show too. Seasons 3 and especially 4 kinda hiccup on the quality, but it's a better fantasy adventure with a wacky cast than 90% of modern isekai. The Lina & Naga the Serpent adventures in the OVA also have their moments, especially in "the Book of Spells" - that one actually gives Naga more of a character than "Scantly clad agent of Chaos and foil to Lina".
Also: Xellos my beloved.
The Light Novel is still ongoing, Volumes 16 and 17 being published after a 7 year hiatus (18 for the main series) and there's been a resurgence in old anime projects (like the City Hunter and Slam Dunk movies, or the return to directing of Ryosuke Takahashi) so maybe there's some faint hope for a Season 6 or a similar project while the voice actors are still not old enough that their voices decline.
I remember it being good but I watched it a long time ago on VHS. Perhaps its time to revisit it if its still ongoing in some way.
Well, it's not. The last season was in 2009.
I was just engaging in some wishful thinking.