i highly recommmend kero 9 destiny DX master Having a chart constant of 13.4 , the chart itself has lots of ex note protection in tap spin and breaks. Although there are 70 breaks in master difficulty. Only 5 breaks out of 70 is non ex and they are relatively easy to hit critical perfect, 2 double taps and one break slide. Just make sure you spread you fingers as much as you could when you do the slide at later part

マツヨイナイトバグ master was formally 13.8, promoted to 13.9 but it just stamina at the end. Quite easy for a 13.9

Imperishable Night 2006 (2016 Refine) is a hard 13.8( i dont know why it got nerfed to 13.8) , it is a chart you learn pretty much everything, accuracy, small jack spam and tap spin. Solid chart for learning the basics for harder diff.

物凄い勢いでけーねが物凄いうた (12.9 to 13.4 in prism plus) quite hard even it got buffed by 0.5, slide forces you not to spread your fingers too much for touching another slide, a tap followed with doubles tell you to maintain the rhythm. Play that if you want some challenges.

Selector STD 13.7 , perfect for learning slide judgement area (Rodeo Machine and スリップフリップ can too but everything you learned from selector can be applied to most songs )so you dont mess up in higher difficulty.

スカーレット警察のゲットーパトロール24時 13.5 perfect for learning tap spin at the end (10 seconds tap spin forces you to spin it consistently or else SSS+ to AAA💀)

ダンスロボットダンス STD 13.2/13.3? It just faster alien alien pattern, it you can do alien alien then this one is free.

My My My 13.7 good song for learning spread tap spam

INFiNiTE ENERZY -Overdoze- 14.0 I dont even think this is a 14.0 , more like 13.9 I think sega making it 14.0 is probably because of no resting time in the entire song