This is the skill tree build I used in my newest route and consider optimal, so you don't have to watch through my whole run to get this information. Let me know if you'd like more clarification on why these are chosen or have questions about other things and I can update this guide or make more!

Level 2

• Enhanced Dodge - Rank 1
• Seals of Death - Rank 1

Level 3

• Air Dodge
• Ki Regeneration - Rank 1

Level 4

• Martial Mastery - Rank 1
• Air Slash

Level 5

• Death Eater - Rank 1
• Thanatos Mastery - Rank 1

Level 6

• Thanatos Mastery - Rank 2
• Death Incarnated

Level 7

• Immortal
• Death Pillar

Level 8

• Martial Mastery - Rank 2
• Critical Boost - Rank 1