If you loved Assassination Classroom the Movie: 365 Days' Time, try Fighting Spirit: Champion Road
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Assassination Classroom the Movie: 365 Days' Time
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Fighting Spirit: Champion Road
What they share
Theyboth carry the playful, uplifting mood tags, and they sit in Action / Animation / Comedy territory. If that's the register that drew you to Assassination Classroom the Movie: 365 Days' Time, the second film will land in a comparable space — through a different lens.
playfuluplifting
What Fighting Spirit: Champion Road is
Here's a boxing anime that really wants you to root for its underdog. Featherweight champ Ippo must defend his title against a med student also after his girl. The presence of old rivals adds some spice, but mostly this just wants to get you pumped.