Day 1
Land at KIX, settle in Osaka, dive into Dōtonbori
Morning
Land at Kansai. Buy an ICOCA at the station (¥500 deposit), load ¥3,000. Take the Nankai Rapi:t express to Namba (40 min, ¥1,490). Drop bags at hotel. Most hotels in Namba/Shinsaibashi are walkable to Dōtonbori.
Afternoon
Osaka Castle. Twenty minutes by subway from Namba. The interior is a 1990s reconstruction and frankly mediocre, but the outer moat, stone walls, and grounds are genuinely impressive — allow 90 minutes total and skip the museum unless it's raining. Walk back through Tenma if you want to see a real Osakan shōtengai (covered shopping arcade).
Evening
Dōtonbori. Takoyaki at any stand without a queue (the famous ones with queues are the tourist tax). Kushikatsu (deep-fried skewers) at a counter shop in Shinsekai if you want the harder-to-find Osakan classic. Beer along the canal until 22:00. Don't double-dip the kushikatsu sauce — it's a shared communal pot.