Reinstall gentoo record:

prepare disk

Disk /dev/sdb: 223.6 GiB, 240057409536 bytes, 468862128 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 19FC4662-CDC6-44A2-A78B-717085B89743

Device         Start       End   Sectors  Size Type
/dev/sdb1       2048    616447    614400  300M Windows recovery environment
/dev/sdb2     616448    821247    204800  100M EFI System
/dev/sdb3     821248   1083391    262144  128M Microsoft reserved
/dev/sdb4    1083392 168855551 167772160   80G Microsoft basic data
/dev/sdb5  168855552 378570751 209715200  100G Microsoft basic data
/dev/sdb6  378570752 378775551    204800  100M Linux filesystem
/dev/sdb7  378775552 382969855   4194304    2G Linux swap
/dev/sdb8  382969856 403941375  20971520   10G Linux filesystem
/dev/sdb9  403941376 468862094  64920719   31G Linux filesystem

mount /dev/sdb9 /mnt/gentoo
rm -rf /mnt/gentoo/*
mkdir home boot
mount /dev/sdb6 /mnt/gentoo/boot
mount /dev/sdb8 /mnt/gentoo/home
rm -rf /mnt/gentoo/boot/*

livecd ~ # mkfs.ext2 /dev/sdb6
mke2fs 1.43.1 (08-Jun-2016)
/dev/sdb6 contains a ext2 file system labelled 'boot'
        last mounted on /boot on Thu Dec 29 21:09:49 2016
Proceed anyway? (y,n) y 
Discarding device blocks: done                            
Creating filesystem with 102400 1k blocks and 25688 inodes
Filesystem UUID: 667051f1-6014-4661-8aac-ff520f78c8f9
Superblock backups stored on blocks: 
        8193, 24577, 40961, 57345, 73729

Allocating group tables: done                            
Writing inode tables: done                            
Writing superblocks and filesystem accounting information: done 

livecd ~ # mkfs.ext4 /dev/sdb9
mke2fs 1.43.1 (08-Jun-2016)
/dev/sdb9 contains a ext4 file system labelled 'gentoo'
        last mounted on / on Thu Dec 29 21:08:00 2016
Proceed anyway? (y,n) y
Discarding device blocks: done                            
Creating filesystem with 8115089 4k blocks and 2031616 inodes
Filesystem UUID: d314e554-3e1c-470d-b90d-0be9214e0114
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

stage3